Thematic Bible: Why moses allowed divorce

They said to Him, Why then did Moses command [us] to give a certificate of divorce and thus to dismiss and repudiate a wife? He said to them, Because of the hardness (stubbornness and perversity) of your hearts Moses permitted you to dismiss and repudiate and divorce your wives; but from the beginning it has not been so [ordained].

And some Pharisees came up, and, in order to test Him and try to find a weakness in Him, asked, Is it lawful for a man to dismiss and repudiate and divorce his wife? He answered them, What did Moses command you? They replied, Moses allowed a man to write a bill of divorce and to put her away. read more.
But Jesus said to them, Because of your hardness of heart [ your condition of insensibility to the call of God] he wrote you this precept in your Law. But from the beginning of creation God made them male and female.