"And Pharisees came up to him and tested him by asking, 'Is it lawful to divorce one's wife for any cause?' He answered, 'Have you not read that he who made them from the beginning made them male and female,, and said, 'For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh'? So they are no longer two but one flesh. What therefore God has joined together, let not man put asunder.' They said to him, 'Why then did Moses command one to give a certificate of divorce, and to put her away?' He said to them, 'For your hardness of heart Moses allowed you to divorce your wives, but from the beginning it was not so'" (Mt 19:3ff., cf. also Mk 10:2ff.).Source: Of the unity and the Indissolubility of Marriage
Christ did not accept the discussion at the level at which his interlocutors tried to introduce it. In a certain sense he did not approve of the dimension that they tried to give the problem. He avoided getting caught up in juridico-casuistical controversies. On the contrary, he referred twice to "the beginning." Acting in this way, he made a clear reference to the relative words in Genesis, which his interlocutors too knew by heart. From those words of the ancient revelation, Christ drew the conclusion and the talk ended.
From the beginning
"The beginning" means, therefore, that which Genesis speaks about. Christ quoted Genesis 1:27 in summary form: "In the beginning the Creator made them male and female." The original passage reads textually as follows: "God created man in his own image; in the image of God he created him; male and female he created them." Subsequently, the Master referred to Genesis 2:24: "Therefore, a man leaves his father and his mother and cleaves to his wife, and they become one flesh." Quoting these words almost in full, Christ gave them an even more explicit normative meaning (since it could be supported that in Genesis they express de facto statements: "leaves. cleaves. they become one flesh"). The normative meaning is plausible since Christ did not confine himself only to the quotation itself, but added: "So they are no longer two but one flesh. What therefore God has joined together, let not man put asunder." That "let not man put asunder" is decisive. In the light of these words of Christ, Genesis 2:24 sets forth the principle of the unity and indissolubility of marriage as the very content of the Word of God, expressed in the most ancient revelation.
The eternal law
It could be maintained at this point that the problem is exhausted, that Jesus Christ's words confirm the eternal law formulated and set up by God from "the beginning" as the creation of man. It might also seem that the Master, confirming this original law of the Creator, did nothing but establish exclusively his own normative meaning, referring to the authority itself of the first Legislator. However, that significant expression "from the beginning," repeated twice, clearly induced his interlocutors to reflect on the way in which man was formed in the mystery of creation, precisely as "male and female," in order to understand correctly the normative sense of the words of Genesis. This is no less valid for the people of today than for those of that time.
JOHN PAUL II'S THEOLOGY OF THE BODY