Throughout the centuries, the Church has meditated on Mary's cooperation in the work of Salvation by deepening its understanding of her association to Christ's redeeming sacrifice.
St Augustine in his own time already gave the Virgin the title of "cooperator" of Redemption (cf De Sancta Virginitate, 6; PL 40, 399).
This title underlines Mary's joint and subordinated action to Christ the Redeemer
Further work on the subject has used the same premises, particularly from the 15th century on. Some feared that Mary would be elevated to the same level as Christ.
In reality the Church teaches clearly the difference between the Mother and the Son in the work of Salvation by illustrating the Virgin's subordination to the One Redeemer, as cooperator. Besides, when the apostle Paul states that "we are God's cooperators" (I Cor 1:9) he asserts the concrete possibility for man to cooperate with God. The collaboration of the faithful, which evidently doesn't make them equal to God in any way, is manifest in the people who preach the Gospel and their personal contribution of trying to plant it in human hearts.
We are all "cooperators in the work of Christ's Salvation," but applied to Mary though, the term of "cooperator" holds a particular meaning
The collaboration of Christians to the Salvation is realized after the events of the Calvary, and they commit themselves to spread its fruit through prayer and sacrifice. On the other hand, Mary's contribution happened at the time of the event and in her capacity as Mother; it covers thus the totality of Christ's salvific work. She alone was associated in such manner to the redeeming offering that brought salvation to all men. In union with Christ and subject to Him, she collaborated to obtain the grace of salvation for all humanity.
The particular role of cooperator accomplished by the Virgin is based on her divine maternity. By giving birth to Whom was destined to realize the redemption of the world, by feeding Him, by presenting Him to the temple, by suffering with Him when He died on the Cross, she "brought to the work of the Savior an absolutely incomparable cooperation" (Lumen gentium, 61). Even though God's call to collaborate in the work of salvation concerns each human being, the participation of the Savior's Mother in the Redemption of humanity represents a unique, unparalleled fact.
In spite of the singularity of her condition, Mary too is the beneficiary of Salvation. She is the first to be the object of the Redemption, redeemed by Christ "in the most sublime way" in her Immaculate Conception (cf Bulla Ineffabilis Deus, in Pio IX Acta I, 605) and filled with the grace of the Holy Spirit.
This last statement leads us now to ask: what does Mary's singular cooperation to the plan of Salvation mean?
The answer is to be found in God's special intention towards the Mother of the Redeemer, whom Jesus calls, in two solemn occasions, Cana and the foot of the Cross, with this special title of "Woman" (cf Jn 2:4; 19:26).
As a woman, Mary is associated to the salvific work
Having created man "man and woman" (Gn 1:27), the Lord wanted to unite in the Redemption as well the new Adam and the new Eve. The progenitors' couple had sinned; a new couple, the Son of God with the collaboration of the Mother, was to reestablish the human race in its original dignity.
Mary, the new Eve, thus becomes a perfect icon of the Church
In the divine plan, she represents at the foot of the Cross the redeemed humanity who, needing salvation, becomes capable of offering a contribution to the development of the salvific work.
Saint John Paul II,
Catechesis, April 9, 1997, § 1.2.3.