‘He’s having an affair.’
‘She’s having a fling.’
‘He’s got a bit on the side.’
‘She’s carrying on with someone else.’

These expressions which people use are more acceptable than using the phrase ‘committing adultery’, which sounds very harsh, but they mean the same thing in the end.
To have an affair, to have a bit on the side, to be unfaithful to your husband or wife, is to commit adultery. If you are married, sleeping with a married man or woman to whom you are not married is going to break your marriage vows. And that, God says, is a sin.

The Bible calls sleeping around before you are married, with someone who is not yet married, ‘fornication’. The word ‘adultery’ refers to sexual relations between two people when both of them, or either of them, is married to someone else. God forbids us to do this. He expects us to keep our marriage vows and he expects us to respect someone else’s marriage vows. ‘Do not commit adultery’ is a fence that God has put around marriage. There is safety and security inside.

Many people think that committing adultery, if it is a sin at all, is sinning against the other person’s husband or wife. This is true. When a person commits adultery, he/she is stealing someone else’s partner. But the Bible also tells us that committing adultery is sinning against God, first and foremost. Joseph, under extreme pressure and being constantly seduced by Potiphar’s wife, says to her, ‘How can I do this great wickedness and sin against God?’ His story is written in the Bible and also in Lloyd Webber’s musical ‘Joseph and the Amazing Technicolour Dreamcoat’. King David, when his adultery with Bathsheba was discovered, said this in his prayer of repentance to God, ‘Against You, You only, have I sinned and done this evil in Your sight.’ His story has been made famous, not only in the Bible, but also in Leonard Cohen’s song ‘Hallelujah’.

The fifth commandment does not, therefore, forbid killing of any sort. God allows us to go to war, He allows us to kill to eat, He commands the government to use the death penalty against murderers and He allows us to defend ourselves from attack. But He forbids the unlawful killing of another human being – you shall not commit murder.

Jesus makes things even tougher for us than the Ten Commandments did. He tells us that the thought is as bad as the deed. If anyone looks on another to lust after them, He said, he/she has already committed adultery in the heart. That, too, is sin. The thought is father to the deed. Someone was once told that a married man or woman was ‘off the menu’. He replied, ‘Maybe so, but can’t I at least look at the menu?’ The answer is, No.