Jesus points out that God allowed divorce to be placed in the code of law to accommodate the hearts of the Israelites. God knew their hearts, he knew that as sinful people they would be unable to maintain the perfect standard so he gave them a rule by which marital separation was to take place whereby the needs and rights of both parties would be cared for. The hardness of the hearts of men and women is what led God to allow divorce. Jesus reminds the Pharisees that from the beginning God intended a man and woman to stay together because the way he created them causes them to become one flesh together at marriage. Furthermore Jesus leaves no room for people to scheme and plan how to leave on partner to join together with another, this was clearly wrong. Divorce did not nullify the fact that men and women become one flesh at marriage, this remained and needed to be respected.
It is sinful attitudes that lead to divorce and as long as those sinful attitudes are held onto marital rupture is going to happen. However just like any sinful practice, thought or attitude there is hope found in repentance. Hard hearts are softened and transformation is allowed to take place. This is the atmosphere within which the Holy Spirit, the Counsellor sent by God, is able to do His work.
It is remarkable that the passage that follows this discussion on divorce is another passage on the place of children in the Kingdom of God. Children are often the ones who suffer the most in divorce and Jesus in the midst of his discourse on the subject speaks to their importance and unique place in his Kingdom. To get into the Kingdom a heart like that of a little child is required. If couples kept their hearts pure like that of a child wouldn’t things go better in their marriage?
**Note** there is much more written about divorce in Scripture but this is what is written here and these are only my thoughts on this passage not the whole issue of divorce.