His intervention comes amid the ongoing debate over the note Mater populi fidelis, published in November 2025 by the Dicastery for the Doctrine of the Faith, which described the use of this Marian title as “always inopportune.”
Müller presented his position this Thursday, October 8, during the international congress De Maria numquam satis, held at the Augustinianum Patristic Institute in Rome.
The full text of his lecture, titled “The Cooperation of the Blessed Virgin Mary in the Redemption,” has been published by La Nuova Bussola Quotidiana.
“When Mary is called ‘Co-redemptrix’ in Catholic piety and theology, it is not a deceptive attribution or an enthusiastic exaggeration, but an objectively revealed truth,” the German cardinal stated.
He added a particularly significant warning in the current doctrinal context: “This title must not be silenced because of Protestant rejection,” but should be properly explained within the framework of Christ’s redemptive work.
Mary’s cooperation does not diminish Christ’s unique Redemption
Müller’s central argument is based on a fundamental distinction in Catholic theology: Jesus Christ is the sole Redeemer of the world, but the efficacy and perfection of His sacrifice do not exclude the cooperation of creatures whom God has freely willed to associate with His saving work.
For the cardinal, this participation does not imply competition with Christ or attribute to Mary a redemptive capacity independent of her Son. On the contrary, it manifests the greatness of divine grace, which allows man to truly collaborate with God.
“God does not exclude us from the work of Redemption, but includes us, allowing us to participate and collaborate in the work of Redemption and the perfection of humanity,” he explained.
Müller recalled that Saint Thomas Aquinas teaches that God grants creatures the dignity of acting as secondary causes, without diminishing His status as the first cause of all good.
This cooperation reaches an absolutely singular dimension in the Virgin Mary. Her consent at the Annunciation was not, according to the cardinal, a merely passive intervention, but a free response to God’s grace that inseparably linked her to the Incarnation and Christ’s saving work.
The cardinal insisted that Mary’s fiat, pronounced in the name of humanity, cannot be separated from her presence at the foot of the cross. The flesh that Christ offered to the Father for the salvation of the world is the same that He received from His Mother.
A defense of the title against the reservations of Mater populi fidelis
Müller’s statements stand in direct contrast to the position expressed by the Dicastery for the Doctrine of the Faith in the doctrinal note Mater populi fidelis, approved by Leo XIV and published on November 4, 2025.
The document, signed by Cardinal Víctor Manuel Fernández, holds that the term “Co-redemptrix” may obscure the exclusive salvific mediation of Jesus Christ and cause confusion among the faithful.
Therefore, it discourages its use, although it acknowledges Mary’s singular cooperation in the work of her Son.
Müller, without explicitly mentioning the note in the passage dedicated to the title, defends a different conclusion. In his view, the problem does not lie in the traditional expression, but in the need to correctly understand its theological meaning.
The former prefect maintains that Christological titles may be applied analogically to creatures without denying what belongs exclusively to Christ. This is the case, for example, with divine filiation: Jesus Christ is the Son of God by nature, while the baptized receive this condition by adoption and participation in grace.
The same applies, he explained, to mediation. Christ is the sole Mediator between God and men, but priests also participate subordinately in His mediation through sacramental ministry.
Therefore, Müller considers that anyone familiar with the principles of Catholic theology should not find scandal in the analogical use of certain titles applied to the Virgin.
The cardinal also warned against an ecumenism that, in the name of understanding with other Christian confessions, ends up compromising the integrity of Catholic doctrine.
Müller and Burke agree in reclaiming Mary Co-redemptrix
Müller’s intervention comes one day after Cardinal Raymond Leo Burke also reclaimed the title of Co-redemptrix during the opening of the congress in Rome.
Burke had warned that fear of misinterpretations should not lead to weakening the traditional teaching on the Virgin’s cooperation in the Redemption.
Both cardinals agree in defending that the uniqueness of Christ’s sacrifice does not prevent recognition of a true, though entirely subordinate, participation of His Mother in the work of salvation.
Müller reinforced this thesis by appealing to the teaching of Saint Irenaeus of Lyons, who contrasted the disobedience of Eve with the obedience of Mary. While the former contributed to the entry of sin and death into the world, the latter, through her faith, cooperated in the coming of the Savior.
The cardinal also recalled that doctrinal development cannot be judged solely by the date on which a particular theological expression appears. The fact that a term was formulated centuries after the biblical events does not, in itself, mean that its content is foreign to Revelation.
In this regard, he rejected the argument that the title of Co-redemptrix should be discarded because of its relatively late appearance in the history of theology.
The intervention of the former Prefect of the Doctrine of the Faith thus adds a new voice to the debate opened by Mater populi fidelis.
In contrast to the Dicastery’s caution, Müller claims the theological legitimacy of a title rooted in Marian tradition and maintains that the singular cooperation of the Blessed Virgin in the Redemption must be explained and defended, not silenced for fear of mistaken interpretations.