Matthew 19:4
And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female, And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female,
When asked about divorce, the reply begins with a question pointing back to what stands written, directing hearers to rely on God's written Word rather than expecting a direct answer to every difficult question. The appeal to the One who made them at the beginning making them male and female grounds marriage in creation, showing that God made humanity male and female at the start. That arrangement began with Adam and one wife, and in that beginning was established the order and law for all who would live upon the earth.
Marriage is from creation, constituted by God as a divine institution and ordinance, with the marriage institution made in Eden. It stands as firm as the Sabbath of the fourth commandment, which was also instituted in Eden when the foundations of the world were laid, when the morning stars sang together and all the sons of God shouted for joy. By attending the wedding feast and by honoring the marriage covenant throughout His ministry, Jesus affirmed and sanctioned marriage, treated it with marked respect, and used it to illustrate important truths.
The marriage vow remains binding in the sight of God under the higher law, so that a husband and wife legally divorced under the laws of the land are still husband and wife in Bible light according to the laws of God. Its vows are not to be lightly set aside, and neither loss of affection, nor advice to separate, nor even a husband's deception by itself gives grounds for divorce. Adultery is the only cause and the only sin God gave by which a husband or wife may be placed where they are free from the marriage vow in God's sight and may leave the spouse. Without a legal divorce on the ground of her husband's guilt of adultery, a woman has no right to marry another man and is not free to marry again, but if she obtains a legal divorce on that ground she is free to be married to whom she chooses.