For the Synoptic authors, especially Matthew,  Torah is the law of God. That's why Mat 16 par is so striking: Jesus is making ineffective the law of God! Still, even Matthew (19:9l 5:32) has the exception of porneia, which, as noted above, means any kind of sexual depravity, including marital violence.  It is also significant that the entire passage seems to be directed to men who in divorcing their wives, force them into beggary or worse. The harness of heart would then apply to the divorcing men, who fail in empathy and love. Women are simply never addressed because they have no legal rights in regard to marriage. Exceptions were added in the Pastorals. but the church never entered into discussions of the legality of marriage until somewhere in the thirteenth century. For those thirteen thousand years people married according to Roman law or the law of the state after Rome fell--patriarchal laws.