Jesus deals with divorce and remarriage in Matthew 5:31-32 and 19:3-23, Mark 10:2-12 and Luke 16:18. His teaching was in response to the Pharisees' question about Deuteronomy 24:1-4. His answer quotes Genesis 1:27 and 2:24. The references are from the Torah which is the Law from the first five books of the Old Testament.

Matthew 5:32 says "'everyone who divorces his wife . . . makes her commit adultery.'" The Pharisees tested Jesus on this because it seemed to contradict Moses' permission to divorce in Deuteronomy 24:1. In Matthew 19:3 they asked "'Is it lawful?'" Their question on the subject is logical because in a similar Luke 16:18 context there is a connection regarding the Law. Luke 16:17 says "'it is easier for heaven and earth to pass away than for one stroke of a letter of the Law to fail.'" Was the Pharisees' purpose to get Jesus embroiled in controversy regarding divorce for "'any reason at all'" (Mt 19:3)? Perhaps the test was if Jesus said Moses was wrong then he would be seen as invalidating the Old Testament.

Jesus' response to their question was "'Have you not read?'" (Mt 19:4). He then refers them to Genesis. God's will is expressed in creation. Similarly his commandments communicate his intentions. So when you are in agreement "this is the love of God, that we keep His commandments" (1Jo 5:3). It becomes a matter of attitude and "doing the will of God from your heart" (Eph 6:6). It is indeed a matter of the heart. Jesus explained that the reason Moses gave was "because of your hardness of heart" (Mt 19:8).