This being said, however, the titles of "co-Redeemer", "co-Redemptrix" and "co-Redemptress" are intrinsically heretical in and of themselves, since they impute "Redeemer-hood" to someone other than He who alone may be called by such a title, as it is a dogma of the Catholic Faith that Jesus Christ alone is our Redeemer.
Here are the false teachings of the false "popes" of the Pre-Vatican II post-Catholic church:
Antipope Leo XIII, Iucunda Semper Expectatione, On the Rosary, 8 September 1894, Sections 2-5: "For in the Rosary all the part that Mary took as our co-Redemptress comes to us, as it were, set forth, and in such wise as though the facts were even then taking place; and this with much profit to our piety, whether in the contemplation of the succeeding sacred mysteries, or in the prayers which we speak and repeat with the lips."
Antipope Benedict XV, Inter Sodalicia, March 22, 1918: "As she suffered and almost died together with her suffering and dying Son, so she surrendered her mother's rights over her Son for the salvation of the human race. And to satisfy the justice of God she sacrificed her Son, as well as she could, so that it may justly be said that she together with Christ has redeemed the human race."
The Blessed Virgin Mary, as worthy of honour and veneration as she is, above all creation, did NOT redeem the human race at all. She participated in the redemption by providing the human flesh, which nature Christ took from her, but she did not redeem the human race with Him. Anything that she merits for us, or that we merit through her intercession, can only be merited because Jesus Christ's perfect sacrifice was of infinite value, without which valuable sacrifice we and Mary could merit nothing.
Being so closely united to Christ in His sufferings, however, it is fitting, though not owed to her, that Mary should be elevated in glory beyond any human being other than Christ Himself, but to say that Mary is our redeemer, that she redeems anyone, in any way is heretical, even if it is with and subordinated to Christ, since this renders the decree from Trent false, which says that Christ alone is our Redeemer.
Therefore it may not justly be said that Mary together with Christ has redeemed the human race, because according to justice, only God could make such a purchase (you cannot demand a purchase unless it is OWED to you in strict justice), with the fitting price of His human blood and the intrinsic and infinite merit and value of the Divinity of the same, nor are we all "co-Redeemers".
Antipope Pius XII expanded even further on the term invented by Antipope Leo XIII in the following teaching:
Antipope Pius XII, Mystici Corporis Christi, #110, 1943: "It was she, the second Eve, who, free from all sin, original or personal, and always most intimately united with her Son, offered Him on Golgotha to the Eternal Father for all the children of Adam, sin-stained by his unhappy fall, and her mother's rights and mother's love were included in the holocaust. Thus she who, according to the flesh, was the mother of our Head, through the added title of pain and glory became, according to the Spirit, the mother of all His members. She it was who through her powerful prayers obtained that the Spirit of our Divine Redeemer, already given on the Cross, should be bestowed, accompanied by miraculous gifts, on the newly founded Church at Pentecost; and finally bearing with courage and confidence the tremendous burden of her sorrows and desolation, she, truly the Queen of Martyrs, more than all the faithful "filled up those things that are wanting of the sufferings of Christ . . . for His Body, which is the Church";"
It is true that the merits of the saints supply "those things that are wanting of the sufferings of Christ for His Body, which is the Church". But note very carefully that St. Paul says "for His Body, which is the Church". Truly, NOBODY is in the Church until the objective redemption performed by Jesus Christ has been applied to his own individual soul. But once a man receives baptism, which is the power of Christ's death and resurrection, he is sanctified and needs not offer any work of satisfaction of his own in order to go thence to heaven. In other words, there is nothing wanting in Christ's sufferings to bring a soul into the Church. But there are some who sin after receiving this great grace, and these must confess and then do PENANCE.
When someone has sinned in such a manner, they are again able to be sanctified by the power of Christ's blood, but NOW THEY OWE A DEBT OF PUNISHMENT. This is where the merits of the saints may be of assistance to souls, when they have fallen after Baptism.
But again, Pius XII words clearly teach that there was something wanting of the sufferings by which Christ effected the objective redemption of souls. But that is heresy in direct opposition to the Council of Florence.
None may hold that the Virgin's sacrifice of suffering was necessary for our salvation, nor that it contributed at all towards the objective redemption of the souls of men, the cancellation of sins, or the opening of the gates of heaven to man. It was meritorious to herself, and built up a wealth of divine favour that she may communicate to men (as also did the sacrifices of the saints and martyrs in the communion of saints), but no matter how good your intention may be in desiring to praise the Holy Virgin, you are NEVER to grieve her by ascribing something to her that her Son's own Church has clearly declared as being His alone, and which she would never claim of herself.
St. Thomas Aquinas, Prima Secundae Partis, Q. 84, Art. 4, Obj. 5: "That a man commit a sin with a good intention, seems to point to ignorance, in so far as he knows not that evil should not be done that good may come of it"
What Must You Do To Get to Heaven?