Divorce and adultery is discussed in the Beatitudes in Matthew 5:31-32. What can be learned from the context? The grouping begins by Jesus saying "'unless your righteousness surpasses that of the scribes and Pharisees, you will not enter the kingdom of heaven'" (Mt 5:20). The section concludes by Jesus saying "'Therefore, you are to be perfect, as your heavenly Father is perfect'" (:48). There are six divisions in the grouping and each deals with an Old Testament command:
A pattern is established with each, beginning with "'You have heard'" and followed by "'But I say to you.'" There is a similarity with Jesus' dialog with the Pharisees. He began with "'Have you not read?'" (Mt 19:4) and continued with "'And I say to you'" (:9). The impression is that Jesus is appending his teaching to the original law.
There is a pattern in each group. Examples increase in severity which result in comparable exercise of judgment. It is remindful of James 1:15 where lustful thoughts lead to sinful actions which lead to death. Verses 21-26 are about anger. The parts deal with anger at a brother (:21), deliberate verbalization against someone (:22), and damaging criticism (:22). With the first there is only nominal sentencing, but with the next you are arrested and taken to court (i.e. the Sanhedrin). Then the most serious results in being in danger of "fiery hell" (:22). The last is the worst because "you will not enter the kingdom of heaven" (:20). Sin prevents it. Therefore it had better be forgiven or else. That's why "if anyone sins, we have an Advocate with the Father" (1Jn 2:1).
Matthew 5:27-30 discusses adultery. The sections are adultery in the heart (:27), violation with the right eye (:29), and sin involving the hand (:30). The eye snippet reminds one of "having eyes full of adultery that never cease from sin" (2Pe 2:14). Verses 33-37 deal with oaths. The parts deal with swearing in general (:33), swearing by the head (:36), and unlimited swearing (:37). Is not a marriage covenant taken by an oath of faith?
Each antithesis starts with the reaffirmation of an Old Testament command. Jesus said "'I did not come to abolish [the Law] but to fulfill'" (Mt 5:17). But then the antithesis builds announcing a goal which may seem unachievable. For instance verse 28 says that lustfully looking at a woman is committing adultery in your heart. It sets a godly standard to demonstrate what is eschatologically expected. Also, you are to go to great lengths to counteract these tendencies. Verse 30 says to cut off a part of your body if it will prevent you from going to heaven.