Theophylact of Ohrid

And when they answered that Moses commanded to divorce a wife, Christ explained to them the Law itself. Moses, He says, was not so merciless as to give such a Law, but he wrote this because of your hardness of heart. Knowing the inhumanity of the Jews, such that a husband who did not love his wife could easily kill her, Moses permitted a husband to divorce an unloved wife.

Commentary on Mark ↗