What did adultery mean to the Jews?
From the King James Version (KJV) of the Bible, Exodus 20:14 spells it out fairly clearly; "Though shall not commit adultery." What did that mean to the Jews? Any discussion on the Bible needs to have all aspects of the context understood. Adultery is a particularly sore spot for most if not all Christian religions. To the Israelites of Moses' day, adultery implied a crime against property. To commit adultery meant to trespass. In their time, the violation meant having sex with a married woman. There existed no prohibition against a married man having sex with a single woman. Adultery could only be committed by a married woman. It is of note what the Law spelled out for men having sex with a single woman (virgin).
Suppose a young woman has never been married and isn't engaged. If a man talks her into having sex, he must pay the bride price and marry her. But if her father refuses to let her marry the man, the bride price must still be paid. (Exodus 22:16-17 CEV)
Note that the "man" in these verses could be single or he could be wed. It did not matter because there was never a prohibition against many wives nor one against sex outside of marriage. Up until Moses gave this law, single women could be taken sexually without regard to their welfare. This began the Creator's return to equality for women. Under the new law, women had to be compensated or taken as brides if they had sex with men. In either case, the women would be taken care of financially.
How about Jesus?
"You have heard that it was said to the ancients: "Do not commit adultery." Ex. 20:14; Deut. 5:18 But I say to you, Everyone looking at a woman to lust after her has already committed adultery with her in his heart." (Matthew 5:27-28 LITV)
This is part of the famous Sermon on the Mount. The sermon was given by Jesus to thousands of followers. Pieces of the sermon are commonly taken out of context repeatedly by those trying to prove Jesus wanted us to follow the Law to the letter. Jesus main point can be gleaned by reading the entire body of Matthew 5. He isn't telling us to follow the letter of the Law to gain acceptance into Heaven. He is telling us to forgo the old Law and follow the new one; to Love each other. If we were to accept the prevailing idea that Jesus was speaking literally then we all need to excise our eyes from their sockets because we are all sinners. Not one of the writings of the New Testament ever indicates any apostle or disciple ever cutting off a hand or plucking out their own eyes. This is because they understood the true meaning of Jesus teaching; Love one another.
Another case taken from John 8 is the woman caught in the act of adultery. I should note that many scholars do not accept the authenticity of this chapter. Notwithstanding, it is a good example of the true teaching of Jesus. The Pharisees brought her to Jesus and tried to trap him by stating what the true punishment should be. The law said clearly that she should be stoned to death. Jesus waited a moment before his now famous retort.
and when they continued asking him, having bent himself back, he said unto them, `The sinless of you--let him first cast the stone at her;' (John 8:7 YLT)
Jesus knew that none of the Pharisees were sinless. They knew it as well and eventually not a single one was left to toss that first rock at the adulteress. Naturally we are all sinners; following the old Law is not a path to salvation. The path to Heaven is through acceptance of Jesus sacrifice. While still on Earth we are to Love God and Love each other. What happened to the woman? Jesus did not forgive her, nor did he accuse her, he told her to leave and sin no more. Many take this to be a condemnation of her act. Again, they overlook the importance of the verse and its context. Everyone sins, so how could this adulteress never sin again? She could not help but sin could she? What Jesus meant is that if she had faith in him, she would be free from the wages of sin no matter what she did.