Fernandez only summarized earlier sources. Ratzinger/Benedict was a key voice.
Co-redemptrix
17. The title “Co-redemptrix” first appeared in the fifteenth century as a correction to the invocation “Redemptrix” (as an abbreviated form of the title, “Mother of the Redeemer”), which had been attributed to Mary since the tenth century. Saint Bernard assigned Mary a role at the foot of the Cross that gave rise to the title “Co-redemptrix,” which first appears in an anonymous fifteenth-century hymn from Salzburg. Although the designation “Redemptrix” persisted throughout the sixteenth and seventeenth centuries, it disappeared entirely in the eighteenth century, having been replaced by the title “Co-redemptrix.” Theological research on Mary’s cooperation in Christ’s Redemption in the first half of the twentieth century led to a deeper understanding of what the title “Co-redemptrix” signifies.
18. Some Popes have used the title “Co-redemptrix” without elaborating much on its meaning. Generally, they have presented the title in two specific ways: in reference to Mary’s divine motherhood (insofar as she, as Mother, made possible the Redemption that Christ accomplished or in reference to her union with Christ at the redemptive Cross. The Second Vatican Council refrained from using the title for dogmatic, pastoral, and ecumenical reasons. Saint John Paul II referred to Mary as “Co-redemptrix” on at least seven occasions, particularly relating this title to the salvific value of our sufferings when they are offered together with the sufferings of Christ, to whom Mary is united especially at the Cross.
19. In the Feria IV meeting on 21 February 1996, Cardinal Joseph Ratzinger, who was the Prefect of the then Congregation for the Doctrine of the Faith, was asked whether the request from the movement Vox Populi Mariae Mediatrici to define a dogma declaring Mary as the “Co-redemptrix” or “Mediatrix of All Graces” was acceptable. In his personal votum, he replied: “Negative. The precise meaning of these titles is not clear, and the doctrine contained in them is not mature. A defined doctrine of divine faith belongs to the Depositum Fidei — that is, to the divine revelation conveyed in Scripture and the apostolic tradition. However, it is not clear how the doctrine expressed in these titles is present in Scripture and the apostolic tradition.” Later, in 2002, he publicly voiced his opinion against the use of the title: “the formula ‘Co-redemptrix’ departs to too great an extent from the language of Scripture and of the Fathers and therefore gives rise to misunderstandings… Everything comes from Him [Christ], as the Letter to the Ephesians and the Letter to the Colossians, in particular, tell us; Mary, too, is everything that she is through Him. The word ‘Co-redemptrix’ would obscure this origin.” While Cardinal Ratzinger did not deny that there may have been good intentions and valuable aspects in the proposal to use this title, he maintained that they were “being expressed in the wrong way.”
20. The then Cardinal Ratzinger referred to the Letters to the Ephesians and to the Colossians, where the vocabulary and the theological dynamism of the hymns present the unique redemptive centrality of the incarnate Son in such a way as to leave no room to add any other form of mediation — for, “every spiritual blessing” is bestowed upon us “in Christ” (Eph 1:3); we are adopted as sons and daughters through him (cf. Eph 1:5); in him we have been graced (cf. Eph 1:6); “we have redemption through his blood” (Eph 1:7); and his grace has been “lavished on us” (Eph 1:8). “In him, we have obtained an inheritance, having been predestined” (Eph 1:11). In him “all the fullness of God was pleased to dwell” (Col 1:19) and for him and through him, God willed “to reconcile all things” (Col 1:20). Such praise for the unique place of Christ calls us to situate every creature in a clearly receptive position in relation to him and to exercise careful, reverent caution whenever proposing any form of possible cooperation with him in the realm of Redemption.
21. On at least three occasions, Pope Francis expressed his clear opposition to using the title “Co-redemptrix,” arguing that Mary “never wished to appropriate anything of her Son for herself. She never presented herself as a co-Savior. No, a disciple.”. Christ’s redemptive work was perfect and needs no addition; therefore, “Our Lady did not want to take away any title from Jesus… She did not ask for herself to be a quasi-redeemer or a co-redeemer: no. There is only one Redeemer, and this title cannot be duplicated.” Christ “is the only Redeemer; there are no co-redeemers with Christ.” For “the sacrifice of the Cross, offered in a spirit of love and obedience, presents the most abundant and infinite satisfaction.” While we are able to extend its effects in the world (cf. Col 1:24), neither the Church nor Mary can replace or perfect the redemptive work of the incarnate Son of God, which was perfect and needs no additions.
22. Given the necessity of explaining Mary’s subordinate role to Christ in the work of Redemption, it is always inappropriate to use the title “Co-redemptrix” to define Mary’s cooperation. This title risks obscuring Christ’s unique salvific mediation and can therefore create confusion and an imbalance in the harmony of the truths of the Christian faith, for “there is salvation in no one else, for there is no other name under heaven given among men by which we must be saved” (Acts 4:12). When an expression requires many, repeated explanations to prevent it from straying from a correct meaning, it does not serve the faith of the People of God and becomes unhelpful. In this case, the expression “Co-redemptrix” does not help extol Mary as the first and foremost collaborator in the work of Redemption and grace, for it carries the risk of eclipsing the exclusive role of Jesus Christ — the Son of God made man for our salvation, who was the only one capable of offering the Father a sacrifice of infinite value — which would not be a true honor to his Mother. Indeed, as the “handmaid of the Lord” (Lk 1:38), Mary directs us to Christ and asks us to “do whatever he tells you” (Jn 2:5).