Matthew 19:8

Because of the hardness of your hearts] The rabbis regarded the liberty of divorce as a special privilege conferred by God upon the chosen people. Rabbi Chananiah said, 'God has not subscribed His name to divorces, except among Israelites, as if He said, I have conceded to the Israelites the right of dismissing their wives; but to the Gentiles I have not conceded it.' Jesus retorts that it is not the privilege, but the infamy and reproach of Israel, that Moses found it necessary to tolerate divorce. Moses allowed it only for the 'hardness of your hearts,' i.e. your unwillingness to accept God's will in the matter of marriage, or, as others explain it, for yolir brutality towards your wives, which would lead you to maltreat them, unless you had the privilege of divorcing them.