Jesus tenderly provides for his mother at His death. It is probable that Joseph, her husband, was long since dead, and that her son Jesus had supported her. Now that He was dying what would become of her? He saw her standing by and knew her cares and griefs, and He saw John standing not far off. So, He established a new relationship between His beloved mother and His beloved disciple. He said to her, "Woman, behold your son, for whom, from now on, you must have a motherly affection," and to John, "Behold you mother, to whom you must pay a sonly duty." And so from that hour, that hour never to be forgotten, that disciple took her to his own home.
Notice the care Christ took of His dear mother. He was not so much taken up with a sense of His sufferings as to forget His friends, all whose concerns He bore. His mother, perhaps, was so taken up with his sufferings that she didn't think of what would become of her, but He did. He had no other way to provide for His mother than by His interest in a friend, which he does here.
He calls her woman, not mother, not out of any disrespect to her, but because mother would have been a cutting word to her who was already wounded with grief. He directs her to look upon John as her son: "Behold him as thy son, who stands there by you, and be as a mother to him."
This was an honor put upon John, and a testimony both to his prudence and to his fidelity. If He who knows all things had not known that John loved Him, He would not have made him Mary’s guardian. It is a great honor to be employed for Christ and to be entrusted with any of His interest in the world.
It was also a great responsibility for John, but he cheerfully accepted it and took her to his own home, not objecting the trouble nor expense, nor his obligations to his own family, nor the ill-will he might contract by it. According to Nicephoras’s Ecclesiastical History (book 2, chapter 3), Mary lived with John at Jerusalem eleven years and then died. Others, however, say she went with him to Ephesus.
Adapted from Matthew Henry's Commentary on the Whole Bible (John 19).