Matthew Poole and continuators on Matthew 19:8

8 He saith unto them, Moses, because of the hardness of your hearts, suffered you to put away your wives: but from the beginning it was not so.

Mark reports this a little differently, Ch. 10.3. As if Christ had first said unto them. What did Moses command you? And they said Moses suffered to write a Bill of Divorcement, and to send her away. And Iesus answered, and said. For the hardness of your Heart, he wrote you this Precept, &c. The substance of our Saviours answer seemeth to be this. Moses gave you no positive Command in the Case, he could not make a Law directly opposite to the Law of my Father. But Moses saw the Wantonness, and Wickedness of your Hearts, that you would turn away your Wives without any just and warrantable Cause, and to restrain your Extravagancies, of Cruelty to your Wives, or disorderly turning them off upon any occasion; he made a Law that none should put away his Wife, but upon a Legal Cognizance of the Cause, and giving her a Bill of Divorce. Indeed possibly this Bill of Divorce was sometimes judicially granted upon irregular Causes, and Moses might connive at it, for the preventing of greater Evils, because you were always an hard Hearted, and Stiff-necked people; and you by your Traditions have expounded that Law, beyond Moses his Intention, and made a Bill of Divorce grantable in Cases which he never thought of, nor intended in that Law. But the measures of Lawfulness, are neither to be taken from Moses his Temporary Toleration and Connivence, nor much less from your Traditions, and Expositions of the Law of Moses, but from the Original Institution of Marriage, and from Gods Original Law relating to it; now God at first made but one Woman for one Man, and so united them, that he stiled them one Flesh: So as he, who puts away his Wife, doth as twere divide, and tear his own Flesh piece from piece, which is Barbarous, Inhumane, and unnatural. And the Law of God was not, that a Man should forsake his Wife, when ever he had a mind to it, but that he should rather forsake his Father and Mother than his Wife, that he should cleave to his Wife living, and dwelling with her, as a Man of knowledge, not hating his own Flesh, Loving his Wife, as his own Body, Loving and Cherishing her, Eph. 5.28.29. Now how can this possibly consist with a Mans putting away his Wife, upon every little and trivial Cause of Offence, or dislike unto her.