Augustine of Hippo

Moses, however, was against a man's dismissing his wife, for he interposed this delay, that a person whose mind was bent on separation, might be deterred by the writing of the bill, and desist; particularly, since, as is related, among the Hebrews, no one was allowed to write Hebrew characters but the scribes. The law therefore wished to send him, whom it ordered to give a bill of divorcement, before he dismissed his wife, to them, who ought to be wise interpreters of the law, and just opponents of quarrel. …

Catena Aurea by Aquinas ↗

Bede

"What," he said, "did Moses command you?" They replied, "Moses permitted a man to write a certificate of divorce and send her away." To which Jesus responded, "It was because of the hardness of your hearts that he wrote you this, etc." What he says is this: Can God be contrary to himself, commanding one thing at first and then breaking his own decree with a new command? It should not be thought so. …

On the Gospel of Mark ↗