Albert Barnes Commentary Matthew 12:46-50

"While he was yet speaking to the multitudes, behold, his mother and his brethren stood without, seeking to speak to him. And one said unto him, Behold, thy mother and thy brethren stand without, seeking to speak to thee. But he answered and said unto him that told him, Who is my mother? and who are my brethren? And he stretched forth his hand towards his disciples, and said, Behold, my mother and my brethren! For whosoever shall do the will of my Father who is in heaven, he is my brother, and sister, and mother." — Matthew 12:46-50 (ASV)

His brethren. There has been some difference of opinion about the persons who were meant here; some supposing that they were children of Mary his mother, others that they were the children of Mary the wife of Cleophas or Alpheus, his cousins, and called brethren according to the customs of the Jews. The natural and obvious meaning is, however, that they were the children of Mary his mother. See also Mark 6:3. To this opinion, moreover, there can be no valid objection.

Who is my mother? There was no lack of affection or respect in Jesus towards his mother, as is proved by his whole life. See especially Luke 2:51 and John 19:25-27. This question was asked merely to fix the attention of the hearers, and to prepare them for the answer; that is, to show them who held the closest and most tender relationship to him. To do this he pointed to his disciples: Dear and tender as were the ties which bound him to his mother and brethren, yet those which bound him to his disciples were more tender and sacred. How great was his love for his disciples, when it was more than even that for his mother! And what a bright illustration of his own doctrine, that we ought to forsake father, and mother, and friends, and houses, and lands, to be his followers.