"And he saith to them, For Moses, at the hardness of your heart, suffered you to forsake your wives; but from the beginning it was not so. And I say to you, that whoever leaveth his wife, but for fornication, and weddeth another, doeth lechery; and he that weddeth the forsaken wife, doeth lechery." - Matthew 19:8-9 (WYC).
The Pharisees understood neither Moses' intention nor Moses' words. Moses' purpose had been to hinder divorces' practice, and to offer to the woman justice by subjecting divorce among the Jews to rules, in order to place marriage on a higher plane.
Moses didn't command that divorces should be obtained. He only made provision to safeguard the woman in case the husband insisted upon a divorce.
Using Mosaic law, Jewish men took wives and chased them away, took others, and regarded marrying and taking wives no differently than trading horses.
If a man had taken a wife, and she didn't please him, he rejected her; and when he'd divorced the first wife, and the second one didn't suit him, he wanted another, or desired his first wife again; thus they multiplied divorces.
Jesus states the reason why Moses had included this provision. Their hearts' hardness, that condition of heart which will seek cruelty against the wife, made such a rule wise. And permission was only implied.
Jesus knew that this method of dealing with the question would prevent greater evils. He said that any man who divorces his wife, except due to adultery, is an adulterer before God; and, similarly, he that marries a woman who has left her husband without Scriptural grounds, is guilty of adultery.