This verse finishes the question Jesus began in Matthew 19:4. Having pointed to how God made the first man and woman, Jesus now quotes what was said about them in Genesis 2:24. The question presses the Pharisees to admit that Scripture describes marriage as a joining, not a contract to be cancelled at will. Barnes draws out Jesus' argument: since husband and wife are so united as to be one, and God made one woman for one man, "it follows that they cannot be separated but by the authority of God." Notice that Jesus says the Creator "said" these words. Gill explains that in Genesis they seem to be the words of Adam (some, he notes, think them the words of Moses as writer), but since they were spoken under divine revelation, they "may be truly affirmed to be said by him," that is, by God.

Jesus answers His own question in the next breath: "Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder" (Matthew 19:6). The Pharisees do not dispute what Genesis says. They raise an objection from Moses instead: "Why did Moses then command to give a writing of divorcement, and to put her away?" (Matthew 19:7).

"Cleave" translates proskollethesetai in the Textus Receptus, "shall be joined to." Barnes says the word denotes "a union of the firmest kind. It is in the original taken from gluing." "Leave father and mother" does not mean abandoning one's parents. Gill says it means quitting "the house of his father and the bed of his mother," as the ancient Aramaic paraphrases of the Old Testament (the Targums) explain it, while still honoring and caring for them.

The word "twain" (two) is worth noticing. Gill points out it is not in the Hebrew text of Genesis 2:24, but it is found in the Septuagint (the ancient Greek translation of the Old Testament) and other early versions, and says it gives the true sense: "neither more nor less can possibly be meant." Barnes explains "one flesh" as one "in law, in feeling, in interest, in affection."

Jesus treats the words of Genesis as the voice of God. Marriage is not only a human arrangement. God is the one who joins (Matthew 19:6). That is why Jesus can say that man must not undo it. The question shows a God who designs relationships with care and stands behind the bond He makes.

Scripture later returns to these same words. Paul quotes Genesis 2:24 when he teaches husbands to love their wives "as their own bodies," and then adds, "This is a great mystery: but I speak concerning Christ and the church" (Ephesians 5:28-32). The one-flesh union Jesus defends here becomes, in Paul's hands, a picture of the faithful love between Christ and His people.