And he answered and said ... - Instead of referring to the opinions of either party, Jesus called their attention to the original design of marriage, to the authority of Moses an authority acknowledged by them both.

Have ye not read? - Genesis 1:27; Genesis 2:21-22. "And said, For this cause," etc., Genesis 2:24. That is, God, at the beginning, made but one man and one woman: their posterity should learn that the original intention of marriage was that a man should have but one wife.

Shall leave his father and mother - This means, shall bind himself more strongly to his wife than he was to his father or mother. The marriage connection is the most tender and endearing of all human relations more tender than even that bond which unites us to a parent.

And shall cleave unto his wife - The word "cleave" denotes a union of the firmest kind. It is in the original taken from gluing, and means so firmly to adhere together that nothing can separate them.

They twain shall be one flesh - That is, they two, or they that were two, shall be united as one - one in law, in feeling, in interest, in affection. They shall no longer have separate interests, but shall act in all things as if they were one - animated by one soul and one wish. The argument of Jesus here is, that since they are so intimately united as to be one, and since in the beginning God made but one woman for one man, it follows that they cannot be separated but by the authority of God. Man may not put away his wife for every cause. What God has joined together man may not put asunder. In this decision he really decided in favor of one of the parties; and it shows that when it was proper, Jesus answered questions without regard to consequences, from whatever cause they might have been proposed, and however much difficulty it might involve him in. Our Lord, in this, also showed consummate wisdom. He answered the question, not from Hillel or Shammai, their teachers, but from Moses, and thus defeated their malice.

Matthew 19:4 Parallel Commentaries

Love Thy Neighbour
I shall notice, first of all, the command; secondly, I shall try and bring some reasons for your obedience to it; and afterwards, I shall draw some suggestions from the law itself. I. First, then, THE COMMAND. It is the second great commandment. The first is, "Thou shalt love the Lord, thy God," and there, the proper standard is, thou shalt love thy God more than thyself. The second commandment is, "Thou shalt love thy neighbour," and the standard there is a little lower, but still preeminently high, …
Charles Haddon Spurgeon—Spurgeon's Sermons Volume 3: 1857

On the Words of the Gospel, "When Jesus had Finished These Sayings," Etc. --S. Matt. xix. 1
On the Words of the Gospel, "When Jesus Had Finished These Sayings," Etc.--S. Matt. xix. 1 I. Jesus Who Chose The Fishermen, Himself also useth a net, and changeth place for place. Why? Not only that He may gain more of those who love God by His visitation; but also, as it seems to me, that He may hallow more places. To the Jews He becomes as a Jew that He may gain the Jews; to them that are under the Law as under the Law, that He may redeem them that are under the Law; to the weak as weak, that …
St. Cyril of Jerusalem—Lectures of S. Cyril of Jerusalem

Eligius, Bishop of Noyon.
THE life of this pious bishop is so much the more worthy our consideration, on account of his having passed many years in the position of an ordinary citizen, before he entered on the clerical office; because his life may thus afford us a picture of the pious citizens of his time. Eligius was born at Chatelàt, a mile from Limoges, A. D. 588. His family had been Christian for many generations, and he received a pious education, [8] the result of which extended throughout his life. In his youth, …
Augustus Neander—Light in the Dark Places