As Jesus has done twice already, He continues to take the law and to show how it is rightly interpreted. He is showing His people what it means to follow after Him. For a third time, He begins, "It was also said..."
Much like our current time, divorce was widely practiced in this culture. And it was seen as morally "OK" since it was "legal." Divorce was all too easy, and Jesus shows us that it is not meant to be that way. When we look at passages such as Genesis 2 and Ephesians 5, we begin to see the weightiness that God puts on marriage. It is meant to be a covenant relationship established by God. Marriage is intended to be one man and one woman in covenant relationship under God for life. And that should not be so easily broken.
Jesus makes it pretty clear in verse 32: "But I say to you that everyone who divorces his wife, except on the ground of sexual immorality, makes her commit adultery, and whoever marries a divorced woman commits adultery." When combined with Jesus' statements in Matthew 19:3-9, we begin to have a clearer view of Biblical marriage. There He takes it all the way back to the beginning of marriage in Genesis 2. Marriage is meant to be for life!
Now, Jesus does give an out. He does not say that all divorce is wrong. There are cases of sexual immorality when the marriage cannot continue further. Jesus gives people the out, saying that sexual immorality is what has torn the relationship asunder (which also shows the high value God places on sex).
At the same time, Jesus does not command divorce. There are cases when the Lord has healed broken marriages, even through sexual immorality. Again, divorce is to be the rare exception, not the rule, among His people. Churches are to see and treat the marriage relationship as sacred. Marriage is meant to be a picture of the Gospel (Ephesians 5)! Therefore, we should treat it with utmost importance, as what we do in our marriage actually shows what we believe about Christ's relationship with us. I would say that marriage is a topic of supreme importance and must be guarded by the Church.
I want to end by saying this: If you have gone through a divorce (or divorces) not condoned by Scripture (which has affected many people in our community), there is still grace. Adultery is NOT the unpardonable sin. While we do not downplay the seriousness of this sin, we also know that Jesus' grace goes deeper. It may be hard for some of you to read passages like Matthew 5:31-32. It may be convicting. But that conviction is meant to lead you to repentance and to Christ's grace. So, while we affirm the sanctity of marriage, we also want to give the hope and healing of Jesus to those who have walked through divorce.