Matthew 19:5

“And said, ‘For this cause shall a man leave his father and mother, and shall cleave to his wife, and the two shall become one flesh?' ”

Indeed that was the only ground on which it was right for a man to leave his father and mother. It was so that he might cleave to his wife with the result that the two became one flesh, united and indivisible. Even filial obedience and family unity, which were so important in Israel, were nevertheless subservient to the fact of the uniting of a male and a female ‘as one flesh'. And by it they became one being in God's eyes (compare Paul's argument in 1 Corinthians 6:16). A man's wife was to become to him more important than anything else apart from God, for she would be a part of himself. (Of course this would not destroy filial obedience and family unity, for it would almost always be done in full agreement with both).

We should note that the verbs are strong ones. ‘Forsake (desert) his father and mother' and ‘cleave closely to (be glued to) his wife'. It was a violent and fundamental change, and resulted in a fundamental alteration in both their lives. From that moment on they had a new focus of concentration, their oneness with one another.