24 Thus we find ourselves at the very center of the fulfillment of the promise contained in the Proto-gospel: the "seed of the woman...will crush the head of the serpent" (cf. Gen. 3:15). By his redemptive death Jesus Christ conquers the evil of sin and death at its very roots. It is significant that, as he speaks to his mother from the Cross, he calls her "woman" and says to her: "Woman, behold your son!" Moreover, he had addressed her by the same term at Cana too (cf. Jn. 2:4). How can one doubt that especially now, on Golgotha, this expression goes to the very heart of the mystery of Mary, and indicates the unique place which she occupies in the whole economy of salvation? As the Council teaches, in Mary "the exalted Daughter of Sion, and after a long expectation of the promise, the times were at length fulfilled and the new dispensation established. All this occurred when the Son of God took a human nature from her, that he might in the mysteries of his flesh free man from sin." The words uttered by Jesus from the Cross signify that the motherhood of her who bore Christ finds a "new" continuation in the Church and through the Church, symbolized and represented by John. In this way, she who as the one "full of grace" was brought into the mystery of Christ in order to be his Mother and thus the Holy Mother of God, through the Church remains in that mystery as "the woman" spoken of by the Book of Genesis (3:15) at the beginning and by the Apocalypse (12:1) at the end of the history of salvation. In accordance with the eternal plan of Providence, Mary's divine motherhood is to be poured out upon the Church, as indicated by statements of Tradition, according to which Mary's "motherhood" of the Church is the reflection and extension of her motherhood of the Son of God. According to the Council the very moment of the Church's birth and full manifestation to the world enables us to glimpse this continuity of Mary's motherhood: "Since it pleased God not to manifest solemnly the mystery of the salvation of the human race until he poured forth the Spirit promised by Christ, we see the Apostles before the day of Pentecost 'continuing with one mind in prayer with the women and Mary the mother of Jesus, and with his brethren' (Acts 1:14). We see Mary prayerfully imploring the gift of the Spirit, who had already overshadowed her in the Annunciation." And so, in the redemptive economy of grace, brought about through the action of the Holy Spirit, there is a unique correspondence between the moment of the Incarnation of the Word and the moment of the birth of the Church. The person who links these two moments is Mary: Mary at Nazareth and Mary in the Upper Room at Jerusalem. In both cases her discreet yet essential presence indicates the path of "birth from the Holy Spirit." Thus she who is present in the mystery of Christ as Mother becomes-by the will of the Son and the power of the Holy Spirit-present in the mystery of the Church. In the Church too she continues to be a maternal presence, as is shown by the words spoken from the Cross: "Woman, behold your son!"; "Behold, your mother."
Source: Redemptoris Mater (Vatican.va)