John Chrysostom

Nevertheless, unspeakable wisdom maketh a defense even for these things, and saith, "Moses for the hardness of your hearts" thus made the law. And not even him doth He suffer to remain under accusation, forasmuch as He had Himself given him the law; but delivers him from the charge, and turns the whole upon their head, as everywhere He doth. …

Homily on the Gospel of Matthew 62 ↗

Theophylact of Ohrid

Then the Lord, turning every accusation upon their own head, defends Moses by saying, "Moses did not set this law in contradiction to God, but rather he addressed this law to your depravity, so that when you in your licentiousness desired to come together with other women, you would not put to death your first wife." For the Israelites, being cruel, would have murdered their wives if they were constrained to keep them. So Moses provided in the law for a writ of divorce to be given to those wives who were hated by their husbands.

Commentary on Matthew ↗

Jerome

He said to them: because Moses allowed you to divorce your wives due to the hardness of your hearts, but it was not like that from the beginning. This is what he meant: Can God be opposed to himself, so that he would command one thing before and then nullify his own command with a new one? It should not be understood this way. …

Commentary on Matthew ↗

Thomas Aquinas

And he said to them. Here he answers the objection. And first he presents the answer; secondly the confirmation, because the Lord proves that a wife should not be put away from the authority of God, which is greater; therefore against the authority of God there is no authority of Moses. But against this: did not the Lord give the law through Moses? See, as the Apostle says in 1 Corinthians 7:25: concerning virgins I have no commandment of the Lord, but I give counsel. …

Commentary on Matthew ↗