John Chrysostom

Knowing therefore these things, let us neither pride ourselves on children that are of good report, unless we have their virtue; nor upon noble fathers, unless we be like them in disposition. For it is possible, both that he who begat a man should not be his father, and that he who did not beget him should be. …

Homily on the Gospel of Matthew 44 ↗

Gregory the Dialogist

The Lord deigned to call faithful disciples His brethren, saying, Go, tell my brethren. Since then a man may be made a brother of the Lord by coming to the faith, it should be enquired how one may become also His mother. Be it known by us then, that he that by believing is made brother or sister of Christ, becomes His mother by preaching; for in pouring Him into the heart of the hearer, he may be said to beget the Lord; and he is made the Lord's mother, when by his word love of the Lord is begotten in the mind …

Catena Aurea by Aquinas ↗

Thomas Aquinas

Hence it says, Whoever does the will of my Father in heaven is my brother, and sister, and mother. For he had a heavenly generation and a temporal one, and he places the heavenly ahead of the temporal. For those who do the will of his Father are related to him according to heavenly generation; hence John (8:39): "If you are the sons of Abraham, do the works of Abraham." For he came to do his will, as John says (4:34, 5:30, 6:38). He says, brother, to indicate the stronger ones and sisters the weaker. But why does he say is my mother? …

Commentary on Matthew ↗