45 Of the essence of motherhood is the fact that it concerns the person. Motherhood always establishes a unique and unrepeatable relationship between two people: between mother and child and between child and mother. Even when the same woman is the mother of many children, her personal relationship with each one of them is of the very essence of motherhood. For each child is generated in a unique and unrepeatable way, and this is true both for the mother and for the child. Each child is surrounded in the same way by that maternal love on which are based the child's development and coming to maturity as a human being. It can be said that motherhood "in the order of grace" preserves the analogy with what "in the order of nature" characterizes the union between mother and child. In the light of this fact it becomes easier to understand why in Christ's testament on Golgotha his Mother's new motherhood is expressed in the singular, in reference to one man: "Behold your son." It can also be said that these same words fully show the reason for the Marian dimension of the life of Christ's disciples. This is true not only of John, who at that hour stood at the foot of the Cross together with his Master's Mother, but it is also true of every disciple of Christ, of every Christian. The Redeemer entrusts his mother to the disciple, and at the same time he gives her to him as his mother. Mary's motherhood, which becomes man's inheritance, is a gift: a gift which Christ himself makes personally to every individual. The Redeemer entrusts Mary to John because he entrusts John to Mary. At the foot of the Cross there begins that special entrusting of humanity to the Mother of Christ, which in the history of the Church has been practiced and expressed in different ways. The same Apostle and Evangelist, after reporting the words addressed by Jesus on the Cross to his Mother and to himself, adds: "And from that hour the disciple took her to his own home" (Jn. 19:27). This statement certainly means that the role of son was attributed to the disciple and that he assumed responsibility for the Mother of his beloved Master. And since Mary was given as a mother to him personally, the statement indicates, even though indirectly, everything expressed by the intimate relationship of a child with its mother. And all of this can be included in the word "entrusting." Such entrusting is the response to a person's love, and in particular to the love of a mother. The Marian dimension of the life of a disciple of Christ is expressed in a special way precisely through this filial entrusting to the Mother of Christ, which began with the testament of the Redeemer on Golgotha. Entrusting himself to Mary in a filial manner, the Christian, like the Apostle John, "welcomes" the Mother of Christ "into his own home" and brings her into everything that makes up his inner life, that is to say into his human and Christian "I": he "took her to his own home." Thus the Christian seeks to be taken into that "maternal charity" with which the Redeemer's Mother "cares for the brethren of her Son," "in whose birth and development she cooperates" in the measure of the gift proper to each one through the power of Christ's Spirit. Thus also is exercised that motherhood in the Spirit which became Mary's role at the foot of the Cross and in the Upper Room.
Source: Redemptoris Mater (Vatican.va)