Co-Redemptrix and Mediatrix of All Graces.
The Lesser-Known Marian Doctrines, Defined and Defended.
Dogma & Infallible Doctrine Vs. Non-Infallible Doctrine
Mary’s role as Mother of God, the Immaculate Conception, the Assumption, and the Perpetual Virginity are all well-known dogmas of the Catholic faith. They are either dogmatically defined or infallible doctrines. However, the doctrines of Mary as Mediatrix and Co-Redemptrix are not dogmatically defined, rather, they are non-infallible doctrine.
The difference between a doctrine which is dogmatic or infallible — even those categories aren’t the same, but I’m lumping them together for the sake of brevity — and a non-infallible dogma can be quickly illustrated in the above chart.
When a doctrine is non-infallible, while it is defined ambiguously in the writings of The Church (be it when the Pope teaches ex-cathedra, or in the tradition of Papal writings, or Church councils), Catholics still have to give some kind of account of the present information, since one definition is yet formally decreed by The Church Herself. This also means not one formulation is binding on all of the faithful.
When a doctrine is dogmatic or infallible, it is formally defined by The Church, Catholics must accept the doctrine as The Church defines it, and such a definition must be taught by the extraordinary magisterium (which is exercised by the Pope’s ability to proclaim infallible doctrine ex-cathedra, or from an ecumenical council), or the ordinary magisterium (which is when a doctrine is continuously defined and taught over multiple church writings).
It must be also be stated that doctrines do not strictly belong in one category or another, but rather they develop over the history of The Church. One example is the immaculate conception, which at one point in time Saints like Thomas Aquinas rejected, but affirmed that she was still made sinless in the womb during the period of animation . This was, according to a pre-scientific understanding, the point in time after conception where a soul was given to a growing fetus. Thomas had more leeway over how to define and understand the holiness of our Lady’s nativity since The Church had yet to give any formal definition to the doctrine. However, after it came to encapsulate the immaculate conception, it entailed Saint Thomas Aquinas did not go far enough.
Ultimately, the doctrine was not fully absent from even Thomas’ writing, nor other theologians who agreed with him, but it was not fully developed at the time since there was no formal ruling or decree on the matter. While they weren’t fully right in neglecting the immaculate nature of the conception, they weren’t far off either, accepting much of the immaculate nature of Mary’s in utero development. It would take time for the doctrine to develop later on. We can see similar developments with the Trinity. The doctrine of the Trinity can be found in scripture.  However, prior to Nicaean Creed, no Church Father, or Biblical verse contained the word “Homoousion” (which means ‘of one’ or ‘same’ being), it was never used to describe the relationship between the persons of the Trinity . Rather it was inferred through deductive evidence.
Defining Mary as Mediatrix & Co-Redemptrix
The best most fully fleshed out definitions of both titled can be found in Vatican II’s document Lumen Gentium. Concerning Mary’s relationship to Christ as “Mediatrix ”, we read,
This maternity of Mary in the order of grace began with the consent which she gave in faith at the Annunciation and which she sustained without wavering beneath the cross, and lasts until the eternal fulfillment of all the elect. Taken up to heaven she did not lay aside this salvific duty, but by her constant intercession continued to bring us the gifts of eternal salvation. By her maternal charity, she cares for the brethren of her Son, who still journey on earth surrounded by dangers and cultics, until they are led into the happiness of their true home. Therefore the Blessed Virgin is invoked by the Church under the titles of Advocate, Auxiliatrix, Adjutrix, and Mediatrix. This, however, is to be so understood that it neither takes away from nor adds anything to the dignity and efficaciousness of Christ the one Mediator. 
In summation, Catholics must hold Mary as mediatrix in the following sense,
(1) Her role does not put her on an equal or greater footing with the mediating and redemptive work of Jesus.
(2) Her role is to work on the behalf of God to distribute his grace to the whole church by taking on the role of Mother of Christ and providing those graces through her heavenly intercession on behalf of the elect.
(3) She acts out her salvific duties from a place of motherly love.
The use of Co-Redemptrix as a term, while not in Lumen Gentium, is alluded to in the following passage,
Thus Mary, a daughter of Adam, consenting to the divine Word, became the mother of Jesus, the one and only Mediator. Embracing God’s salvific will with a full heart and impeded by no sin, she devoted herself totally as a handmaid of the Lord to the person and work of her Son, under Him and with Him, by the grace of almighty God, serving the mystery of redemption. Rightly, therefore, the holy Fathers see her as used by God not merely in a passive way, but as freely cooperating in the work of human salvation through faith and obedience. For, as St. Irenaeus says, she “being obedient, became the cause of salvation for herself and for the whole human race” . 
Here, Catholics affirm the following three truths,
(1) Mary has a non-trivial and unique role in the mystery of redemption.
(2) Mary’s role in the redemption of the world was as an active, not passive, participant.
(3) Mary’s role as Co-Redemptrix does not put her role on an equal or greater footing with mediating and redemptive work of Jesus.
I will be making positive arguments from scripture for each role. I do this not because I believe scripture is the sole infallible rule of faith, but because I would much rather grant as much as I can to appeal to any protestant readers.
Mary as Co-Redemptrix — Proof 1
There are three Biblical Texts that I will use to establish Mary’s role as Co-Redemptrix. The first is from Genesis 3:15. There are four translations.
And I will establish a feud between thee and the woman, between thy offspring and hers; she is to crush thy head, while thou dost lie in ambush at her heels. — Knox Bible
I will put enmity between you and the woman, and between your seed and her seed; he shall bruise your head and you shall bruise his heel.” — RSVCE
I will put enmity between you and the woman, and between your offspring and hers; They will strike at your head, while you strike at their heel. — NABRE
Traditionalist Catholics, following along the Vulgate tradition, translate the pronoun of the “seed” as “she”. This lends itself to seeing the verse as a prophecy about Mary. While the Knox and the DRA both go with this translation, it is not without its reason, as Monginsor Ronald Knox writes, “most manuscripts of the Latin version have ‘she’, which plainly gives a better balance to the sentence”.  Furthermore, Saint Irenaeus himself, giving the earliest non-Biblical commentary of this verse within the Christian tradition, identifies Mary as the one who will bruise the head. 
The majority of Christian translators (including both Catholic and Protestant) support the translation of the pronoun as ‘he’.  It can also be found in the Septuagint tradition.  Lastly, Church Fathers like Saint John Chrysostom used this translation as well,  so it is not out of the bounds of Church Tradition. In this view, Christ is the prophesied Messiah, ready to crush the head of the serpent.
Lastly, when translating the pronoun as ‘they’, many liberal Christians see the text as attributing this act to humanity in general. However, this need not be the only way of reading it, Saint Paul arguably reads the text as referring to The Church as a whole.
then the God of peace will soon crush Satan under your feet. The grace of our Lord Jesus Christ be with you. — Romans 16:20 RSVCE
The multiplicity of possible translations should not be read as precluding one another, but rather we can have 4 readings or interpretations, which are all equally true given the wide-array of translating the pronoun.
Literal: On this reading, God is speaking of humanity’s literal relationship with snakes (the animal Satan took the form of) as a result of the fall. Our collective heel will crush their heads, and he (through his offspring) hurt us as a result of sin (they/they).
Christological: On this reading, God is speaking of Christ coming to directly destroy Satan’s influence in the redemption, and Satan will directly bruise him in the crucifixion (he/he).
Mariological: On this reading, God is speaking of Mary, who is giving birth to Christ. Mary will be bruised indirectly by Satan as she witnesses’ her Son’s death, whereas Mary will indirectly crush Satan by giving birth to Christ, the cause of the redemption (she/she).
Ecclesial: On this reading, God is speaking of the predestined offering in the church, the elect of humanity, who will act as the heel of Christ to crush Satan’s influence (they/they).
As Jimmy Akin says,
There is a sense in which Mary crushed the serpent’s head and in which she was struck at by the serpent. She didn’t do these things directly, but indirectly, through her Son. It was Jesus who directly crushed the serpent’s head from the cross and Jesus whom the serpent directly struck on the cross. Yet Mary cooperated in these events.
She, not anyone else, was the person who agreed to become the human channel through which Christ would enter the world in order to crush the serpent’s head 
It will not do for the protestant to merely claim that there is a preferable interpretation to the Mariological one, but the protestant will have to give positive arguments for why ‘she’ is not an acceptable pronoun translation. Furthermore, even if they were to do this, and he was the exclusive translation, their burden would not be met. To quote the Douay-Rheims commentary,
She shall crush. Ipsa, the woman; so divers of the fathers read this place, conformably to the Latin: others read it ipsum, viz., the seed. The sense is the same: for it is by her seed, Jesus Christ, that the woman crushes the serpent’s head. 
Even if it is the pronoun does refer to the seed, which is the direct cause of the crushing and the biting, Mary is still the indirect cause since it is by her virgin birth whereby the incarnation takes place so that the redemption and the crucifixion take place.
Mary as Co-Redemptrix — Proof 2
In support of the above Mariological interpretation, we read in scripture,
(and a sword will pierce through your own soul also), that thoughts out of many hearts may be revealed — Luke 2:35
Whereas Jesus was directly bruised during his redemptive work, Mary was indirectly bruised, witnessing and experiencing the pain of her son, in person. Her pain was not like our pain, it was a pain that pierced into her very soul. This is a truth Simon says of her and her alone. Mary’s pain is tied to her son’s pain, the bruising of the son is now the bruising of his mother.
Mary as Co-Redemptrix — Proof 3
This proof is more of a probabilistic one. When Mary agreed to be the mother of the Messiah (Luke 1:38), it is reasonable to assume she knew of his death in Isaiah 53:10. This is not a woman unfamiliar with scripture but knows it intimately when she sings her song of praise based on 1 Sam 2.1–10. If she foreknew her son would die, this makes her someone who agreed to undergo the pain her son would, since she knew of her material connection she would bear with her son. If not at the time of the annunciation, then at the time of prophecy.
How Do These Verses Establish Mary as Co-Redemptrix?
(1) Her relationship with Christ as a Mother increases her suffering to a far greater degree than anyone else.
- Inferred from the fact that this is how all mothers in a healthy relationship with their son would have viewed the situation.
(2) Her suffering was prophesied to be of a greater kind than any other human being, going into her very soul.
- Luke 2:35
(3) Her suffering took place indirectly through the cross, rather than after the fact. Mary suffers alongside and through Christ at the cross, whereas all Christians, when we suffer, suffer for the one at the cross.
- Genesis 3:15
(4) She was an active participant in the story of redemption from the beginning of Christ’s incarnation. Unlike those placing Christ on the cross who did not know what they were doing, Mary knew of her role from the beginning.
- Luke 23:34
How does Mary’s role avoid making her an equal to Christ?
(1) Christ is the direct cause of the redemption and the atonement; Mary is the indirect cause of the redemption and the atonement. Her role was unnecessary but nonetheless was given to her out of God’s grace. Christ alone is redeemer, but since Mary acts indirectly to bring about the redemption, she is Co-Redemptrix.
(2) Paul himself says that he offers up additional suffering to make up what is lacking in Christ’s affliction (Colossians 1:24). This does not mean Paul was adding to the redemption, since Paul’s afflictions don’t redeem anyone, but lead people to redemption. If this is the case with Paul, why not Mary?
Biblical Proof for Co-Mediatrix — Proof 1
Mary said yes to the incarnation in Luke 1:38. She says,
And Mary said, “Behold, I am the handmaid of the Lord; let it be to me according to your word.” And the angel departed from her.
The incarnation is the vehicle whereby all graces of salvation come into the world; by saying yes, Mary stands between God and man. Does this mean Mary was necessary? No, remember in Mattew 3:9 Christ reminds the Jews he could create sons of Abraham from stones. It was out of the grace of God he chose Mary to participate.
Biblical Proof for Co-Mediatrix — Proof 2
In the Deuterocanon, we read
And Oni′as spoke, saying, “This is a man who loves the brethren and prays much for the people and the holy city, Jeremiah, the prophet of God.” — 2 Maccabees 15:14
Here the prophet Jeremiah prays for Jerusalem and Oni’as (along with his fellow rebels). For those of my protestant friends who doubt 2 Maccabees as scriptures, remember that Paul himself, in the Book of Hebrews, references this work. There we read,
Women received their dead by resurrection. Some were tortured, refusing to accept release, that they might rise again to a better life. Others suffered mocking and scourging, and even chains and imprisonment — Hebrews 11:35
This is in reference to two events in 2nd Maccabees.
(1) The first part is in reference to 2nd Maccabees 7, where a woman and her sons were tortured and martyred for the sake of returning to life.
(2) The second is in reference to Eleazar in 2nd Maccabees 6:30–31, who died to serve as an example, when he could have renounced his faith and accepted release.
This is confirmed in not only Catholic but also protestant commentaries as well. The Ellicott’s Commentary for English Readers instructs its readers to,
See the account of the aged Eleazar (2 Maccabees 6:30), martyred because he would not pollute himself with swine’s flesh and the “flesh taken from the sacrifice commanded by the king.” The following chapter records the martyrdom of seven brethren, who for their adherence to their law were put to death with cruel tortures. 
The Pulpit Commentary conquers with the first reading part, but not the second. It reads,
The latter part is as evidently suggested at least by the narrative of 2 Macc. 7; where it is recorded how, under the persecution of Antiochus Epiphanes, seven sons of one mother were tortured and put to death 
While it is true Saint Paul does quote non-inspired text in other parts of the Bible, one has to distinguish between citing texts and citing texts as scripture. Paul is citing the history of the Old Testament in the prior verses and makes no distinction when he approaches verse 35, he writes in full,
And what more shall I say? For time would fail me to tell of Gideon, Barak, Samson, Jephthah, of David and Samuel and the prophets — who through faith conquered kingdoms, enforced justice, received promises, stopped the mouths of lions, quenched raging fire, escaped the edge of the sword, won strength out of weakness, became mighty in war, put foreign armies to flight. Women received their dead by resurrection. Some were tortured, refusing to accept release, that they might rise again to a better life. — Hebrews 11:32–35
Notice, this is part of one ongoing sacred history, Paul is not citing the events in Maccabees in exclusion to the Old Testament, but as part of one ongoing testament to the power of faith. Even if we grant Paul doesn’t see the work as infallible, it is at least theologically reliable enough for Paul to use the work to establish doctrines of the faith.
But back to the main point, if Jeremiah is praying for Jerusalem and the people of Israel, we can be far more sure Mary is praying for us, her children in the church.
Biblical Proof for Co-Mediatrix — Proof 3
In terms of Mary acting out of maternal love, we have two additional proofs. First, at the cross, Christ tells her and the Apostle John,
When Jesus saw his mother, and the disciple whom he loved standing near, he said to his mother, “Woman, behold, your son!” Then he said to the disciple, “Behold, your mother!” And from that hour the disciple took her to his own home. — John 19:26–27
Notice here that Mary is given to the care of an apostle, and she is to go to his home. However, this ceases to only be John’s responsibility, in the Book of Acts we read,
Now the company of those who believed were of one heart and soul, and no one said that any of the things which he possessed was his own, but they had everything in common. And with great power the apostles gave their testimony to the resurrection of the Lord Jesus, and great grace was upon them all. There was not a needy person among them, for as many as were possessors of lands or houses sold them, and brought the proceeds of what was sold — John 19:26–27Acts 4:32–34
How could John take care of Mary if he gave away all he had? Simple, the care and welfare of Mary would extend also to the church as a whole. The injunction to care for her would belong to all of us, and she would become our Mother as she was John’s own. In heaven, she would continue to pray for us out of motherly care and the supernatural faith that God had created in her.
Biblical Proof for Co-Mediatrix — Proof 4
The second comes from her role to the church as Mother of Jesus the bridegroom. If the church is the bride of Christ, then Mary acts as a Mother-in-law to the rest of the body. Scripture tells us of many times where the church is the bride of Christ
Revelations 21:9 — Then came one of the seven angels who had the seven bowls full of the seven last plagues, and spoke to me, saying, “Come, I will show you the Bride, the wife of the Lamb.”
2 Corinthians 11:2 — I feel a divine jealousy for you, for I betrothed you to Christ to present you as a pure bride to her one husband.
Ephesians 5:22–24 — Wives, be subject to your husbands, as to the Lord. For the husband is the head of the wife as Christ is the head of the church, his body, and is himself its Savior. As the church is subject to Christ, so let wives also be subject in everything to their husbands.
Mary acts as a Mother-in-law, who loves her daughter-in-law as she loves herself.
How Do These Verses Establish Mary as Mediatrix of All Graces?
(1) Mary mediates between Jesus and man so that the grace Christ wins for us in the atonement is provided to the elect through her intercession.
- 2 Maccabees 15:14
(2) Mary mediates between Jesus and man so that the grace Christ wins for us in the atonement is provided to the elect through saying yes to her role as Mother of God.
- Luke 1:38.
(3) Mary acts from a place of motherly devotion to her son and the church as a mother-in-law.
- Revelations 21:9
- 2 Corinthians 11:2
- Ephesians 5:22–24
(4) Mary acts from a place of motherly devotion to her son and the church as an adopted mother
- John 19:26–27
- Acts 4:32–34
Another Redeemer or Mediator?
Contrary to protestant objections, Mary is not another Redeemer or Mediator, but rather someone who offers up her own contribution to Christ’s act of redemption and mediation. Christ is the sole mediator in relation to the atonement (his ransom on the cross). Mary did not atone for the sins of the world, but acted as an indirect cause of the atonement, extended her own suffering through the ordeal, and offers up all grace by it to the church.
and there is one mediator (mesitēs) between God and men, the man Christ Jesus, who gave himself as a ransom for all, the testimony to which was borne at the proper time — 1 Timothy 2:5–6
Why then the law? It was added because of transgressions, till the offspring should come to whom the promise had been made; and it was ordained by angels through an intermediary (mesitēs). — Galatians 3:19–20
Moses is called a mediator in Galatians, but he is not another mediator in any other relationship. Likewise, Mary is not herself meditating in the sense of providing atonement, but enabling the incarnation.
Furthermore, when using the prefix ‘co’ we make a point of emphasizing that the person is working under the authority of someone else, like a lead author who takes on a co-author. A co-author is not equal to the author, nor even necessary (they might be allowed on board to share credit out of charity)
So neither he who plants nor he who waters is anything, but only God who gives the growth. He who plants and he who waters are equal, and each shall receive his wages according to his labor. For we are God’s fellow workers (sunergos); you are God’s field, God’s building. — 1 Corinthians 3:7–9 (RSVCE)
Other translations make the point clearer,
For we are God’s co-workers. You are God’s farmland and God’s building (ISV)
We are coworkers belonging to God. You are God’s field, God’s building (NET Bible)
For we are God’s coworkers. You are God’s field, God’s building. (CSB)
The word for ‘fellow workers’ is a compound word. According to the Strong’s Concordance,
sunergos — From a presumed compound of sun and the base of ergon; a co-laborer, i.e. Coadjutor — companion in labour, (fellow-)helper(-labourer, -worker), labourer together with, workfellow. 
Here we see that while we are workers along with God, God is the one doing all the work, he gets all the glory, but we act as his instruments.
While Mary is unique in terms of the degree she suffers alongside her son, suffering alongside Christ is something we all do as Christians. As Dave Armstrong chronicles,
Romans 8:17 . . . fellow heirs with Christ, provided we suffer with him in order that we may also be glorified with him.
2 Corinthians 1:5 For as we share abundantly in Christ’s sufferings, so through Christ we share abundantly in comfort too.
2 Corinthians 4:10 always carrying in the body the death of Jesus, so that the life of Jesus may also be manifested in our bodies.
Galatians 2:20 I have been crucified with Christ; it is no longer I who live, but Christ who lives in me; . . .
Galatians 6:17 Henceforth let no man trouble me; for I bear on my body the marks [Gk., stigma] of Jesus.
Philippians 3:10 that I may know him and the power of his resurrection, and may share his sufferings, becoming like him in his death,
Colossians 1:24 Now I rejoice in my sufferings for your sake, and in my flesh I complete what is lacking in Christ’s afflictions for the sake of his body, that is, the church,
2 Timothy 2:11 . . . If we have died with him, we shall also live with him 
If we suffer for and with Jesus so that we may share in his glory, imagine how much Mary shares by suffering as no one has before (Romans 8:17). Imagine her comfort for going along with his pain (2 Cor. 1:5), how manifest he was in her (2 Cor.4:10)? When Mary suffered with Christ, she contributed something in the redemption, not as an equal, but as a loving subordinate from the beginning.
Saint Paul also speaks of providing other Christians salvation as well, through preaching the Gospel,
To the weak I became weak, that I might win the weak. I have become all things to all men, that I might by all means save some — 1 Corinthians 9:22
Preaching is not the only thing that saves, praying for others does as well since it leads to the forgiveness of sins (James 5:15–16), and that’s what Mary does for all believers.
Mary is called Co-Redemptrix because she was the indirect cause of our redemption by suffering alongside her son. Her role was unique because no one else suffered the same pain at the crucifixion of her son, nor said yes to it from the beginning. Her pain was prophecied to take place by Simon when she brought Christ to the temple. Her role makes her son no less a redeemer since all Christians suffer alongside Christ, but she suffered in a way that was unique.
Mary is called Mediatrix because she acted as a stand between Christ and creation in being the vehicle for the incarnation and dispending all grace through prayer. She was not needed but was given her role as a blessing. Her role makes Jesus no less the sole mediator since it is in relation to the atonement, not the incarnation or as an advocate praying so that grace may abound for the elect. Moses was called a mediator, and Paul himself was an instrument of God’s saving grace.
 Jimmy Akin, ‘What is the Difference Between Doctrine and Dogma?’, Link
Rev. John Trigilio, Jr and Rev. Kenneth Brighenti, ‘What Are Extraordinary Magisterium and Ordinary Magisterium?’, Link
 ST III, q. 27, a1, Link
 Dave Armstrong, ‘50 Biblical Evidences for the Holy Trinity’, Link
 Dale Tuggy, ‘History of Trinitarian Doctrines’, Link
 Pope Paul VI, Lumen Gentium, Chapter VIII, Section 3, Paragraph 62, Link
 Pope Paul VI, Lumen Gentium, Chapter VIII, Section 2, Paragraph 56, Link
 Reverend Monsignor Ronald Knox, ‘Genesis 3:15 Commentary’, Link
 Irenaeus, Against Heresies, Book V, Chapter 21, para. 1, Link
 Genesis 3:15, Parallel Translations, Context and Cross Reference, Link
 Genesis 3:15, LXX, Link
 St. John Chrysostom, On Genesis 2:4–3:24, Link
Jimmy Akin, Who Will Crush the Serpent’s Head, Link
 DRA, Genesis 3:15, Commentary, Link
 Rev. W. F. Moulton, D. D., Ellicott’s Commentary for English Readers, ‘Hebrews 11’, Link
 Joseph Exell, The Pulpit Commentary, ‘Hebrews 11’, Link
 Sunergos, Strong’s Exhaustive Concordance, Link
 Dave Armstrong, Seton Magazine, Why Suffering *With* Christ (Not Just For Him) is Biblical, Link