" When Jesus therefore had seen His Mother and the disciple standing whom He loved, He saith to His Mother: 'Woman, behold thy son.' After that, He saith to the disciple: 'Behold thy Mother.' And from that hour, the disciple took her as his own" (John 19: 26-27).
Recall the words of Amos above, "mourning of an only son." This is what the Blessed Virgin Mary felt, not only in losing her divine Son, but in mourning for her adopted children - the entire human race. Oh, what sorrow, what a heart that could encompass this and accept God's will that this all be carried out so that these children would have the opportunity of being with her divine Son in Heaven. She understood the heavenly mandate long before man ever conceptualized the impact of her Son's death. The holy Angelic Doctor of the Church Saint Thomas Aquinas writes in his masterful Summa Theologica 3: 30, 1: "She uttered her yes 'in the name of all human nature'." Another Doctor of the Church Saint Irenaeus writes: "In accordance with this design, Mary the Virgin is found obedient, saying, 'Behold the handmaid of the Lord; be it unto me according to thy world.' But Eve was disobedient; for she did not obey when as yet she was a virgin. And even as she, having indeed a husband, Adam, but being nevertheless as yet a virgin . . . having become disobedient, was made the cause of death, both to herself and to the entire human race; so also did Mary, having a man betrothed (to her), and being nevertheless a virgin, by yielding obedience, become the cause of salvation, both to herself and the whole human race. . . . (And so) the knot of Eve's disobedience was loosed by the obedience of Mary. For what the virgin Eve had bound fast through unbelief, this did the virgin Mary set free through faith." He also added, "For just as the former was led astray by the word of an angel, so that she fled from God when she had transgressed His word; so did the latter, by an angelic communication, receive the glad tidings that she should sustain (portaret) God, being obedient to His word. And if the former did disobey God, yet the latter was persuaded to be obedient to God, in order that the Virgin Mary might become the Patroness (advocata) of the virgin Eve. And thus, as the human race fell into bondage to death by means of a virgin, so is it rescued by a virgin; virginal disobedience having been balanced in the opposite scale by virginal obedience."
Here we have, as St. Irenaeus states, two Eves, two sinless virgins from the sides of two Adams. Both were approached by heavenly spirits created by God - the fallen angel lucifer in the form of the serpent, and the obedient angel Gabriel as the Archangel announcing to Mary the good news and awaiting her fiat. Here we have the struggle in two gardens under two trees - Eden and the Tree of life, Olivet/Calvary and the Tree of death which would overcome death and forever be the Tree of everlasting life whose roots were planted in the only Church Christ established: the holy Catholic Church upon the rock (petras) of Peter (cf. Matthew 16: 18-19). Here we have the experience of labor of two births, both painless in process but carrying great responsibilities once completed - Eve from the rib of Adam, Mary conceived immaculately whose virginal womb was implanted by the Third Person of the Blessed Trinity to gestate the Second Person of the Blessed Trinity at the will of the First Person of the Blessed Trinity. In both Eve and Mary two humanities were brought about in two creations, with two sinless Adams "born" directly from God. Both experience two deaths because of one sin.
The passage above is in perfect compliance with Mosaic Law for Christ was responsible to assure someone would care for His Mother. Upon His death, a younger brother, if there was one, would have been assigned to care for Mary. But since Christ gave Mary into the care of His beloved disciple, it proved there were no other sons to whom He could have entrusted her. John represents the faithful of the Church He established, and Mary the Mother of the Church.