ADULTERY
Adultery means a married person having sexual intercourse with someone who is not their husband or wife. Jesus taught that adultery is wrong. He says that unfaithfulness begins when a person thinks about a person they’re not married to in a lustful way.
Jesus says that sin (doing wrong) isn’t just an action but also the wrong thoughts and desires that we have. The wrong thoughts can lead to the wrong actions.
So Jesus is suggesting that unfaithfulness starts in the heart and mind, that married people shouldn’t even think about another person outside of the marriage.
When Jesus uses the example of “if your eye causes you to sin take it out” he isn’t meaning this literally; he’s trying to make a point that we need to avoid dwelling on thoughts and feelings that are going to lead to unfaithfulness. Lust has a selfish motive as it is about using someone for self-gratification, therefore it is different from love.
DIVORCE
Christians believe that marriage is a covenant relationship, which means one that is based on trust and it reflects the relationship God offers to people with himself. God is faithful, and he wants people to be faithful to him; this extends to human relationships too. Therefore, marriage mirrors the covenant relationship with God, and unfaithfulness in a relationship breaks trust.
Jesus taught in the Sermon on the Mount that divorce is wrong unless it involves one of the partners committing adultery.
You can read more about a Christian response to divorce here or watch an interview with a Christian couple who had to go through previous divorces
It’s important to remember that Jesus both challenged people in his teachings and showed love and grace towards them, as he did to all people who had committed a sin.
ANCIENT ISRAEL CULTURE
The poor treatment of women at the time that Jesus gave this sermon is the reason that he spoke out about adultery and divorce.
In the Old Testament, if a man chose to divorce his wife, he was allowed to give her divorce papers and send her away. However, a woman could not seek a divorce from her husband. Read more in Matthew 19:8.
In fact, women were in a difficult position as they had no real power in society. Women needed to be in a family for their own security, if they were outside the protection of a family they were vulnerable and could easily become penniless and homeless.
The options for women outside of the home were begging, prostitution or death. This was the stark reality facing a woman who was separated from her husband. Husbands could divorce their wives for any reason, so women were very dependent on their husbands.
In the original Hebrew text, it says that God hates ‘putting away’ or kicking the wife into the streets; in English, this gets interpreted as divorce.