Thematic Bible: Why moses allowed divorce

They say to him, Why did Moses then command to give a writing of divorcement, and to put her away? He saith to them, Moses, because of the hardness of your hearts, suffered you to put away your wives: but from the beginning it was not so.

And the Pharisees came to him, and asked him, Is it lawful for a man to put away his wife? tempting him. And he answered and said to them, What did Moses command you? And they said, Moses suffered to write a bill of divorcement, and to put her away. read more.
And Jesus answered and said to them, For the hardness of your heart, he wrote you this precept. But from the beginning of the creation, God made them male and female.