13 And after they were departed, behold an angel of the Lord appeared in sleep to Joseph, saying: Arise, and take the child and his mother, and fly into Egypt: and be there until I shall tell thee. For it will come to pass that Herod will seek the child to destroy him.
Rabanus: Matthew omits the day of purification when the first-born must be presented in the Temple with the lamb, or a pair of turtle doves, or pigeons. Their fear of Herod did not make them bold to transgress the Law, that they should not present the Child in the temple. As soon then as the rumour concerning the Child begins to be spread abroad, the Angel is sent to bid Joseph carry Him into Egypt.
Hilary: The first time when he would teach Joseph that she was lawfully espoused, the Angel called the Virgin his espoused “wife;” but after the birth she is only spoken of as the Mother of Jesus. As wedlock was rightfully imputed to her in her virginity, so virginity is esteemed venerable in her as the mother of Jesus.
Pseudo-Chrysostom: He says not, the Mother and her young Child, but, “the young Child and His mother;” for the Child was not born for the mother, but the mother prepared for the Child.
How is this that the Son of God flies from the face of man? . . . First; He ought to observe, even in this, the law of that human nature which He took on Him; and human nature and infancy must flee before threatening power. Next, that Christians when persecution makes it necessary should not be ashamed to fly. But why into Egypt? The Lord, “who keepeth not His anger for ever,” remembered the woes He had brought upon Egypt, and therefore sent His Son thither, and gives it this sign of great reconciliation, that with this one remedy He might heal the ten plagues of Egypt, and the nation that had been the persecutor of this first-born people, might be the guardian of His first-born Son. As formerly they had cruelly tyrannized, now they might devoutly serve; nor go to the Red Sea to be drowned, but be called to the waters of baptism to receive life.
Scripture from the Douay-Rheims Bible. Commentary from St. Thomas Aquinas, Catena Aurea, Vol. I (London: Rivington, 1842).