Adultery is the sexual unfaithfulness of a husband or a wife; it is literally a married person having sex with another married person, who is not their husband or wife. This is prohibited in the Bible, as stated in the Ten Commandments and reiterated many other times.
Jesus extends the concept adultery from the physical act to the mere thought of it; that is lust. “But I tell you that anyone who looks at a woman lustfully has already committed adultery with her in his heart,” (Matthew 5:28).
Idolatry, covetousness, and apostasy are referred to as spiritual adultery, (Jeremiah 3:6-9 and Hosea 1:2); that is, being unfaithful to God.
The book of Proverbs contains the majority of the Bible’s mentions of the word “adulteress” (seven times in Proverbs compared to five times in the rest of the Bible). An “adulteress” is “a woman who commits adultery,” that is, she has sex with someone other than her husband. In today’s language, that is referred to as “cheating.”
Solomon warns his son — and all men — to stay away from the adulteress.
The Law of Moses notes that both the adulterer (the male participant) and the adulteress (the female participant) should be put to death (Leviticus 20:10). That is how serious God views the breaking of marriage vows.
Although the majority of modern society takes a much more casual perspective on lifelong monogamy, God’s staunch opposition to adultery hasn’t changed. Fortunately, his response has. In the Old Testament (as mentioned above), the prescribed response to adultery is judgment. However, in the New Testament, Jesus — God’s son — demonstrates a kinder, gentler response: mercy (John 8:1-11).
However, remember that even though Jesus will give both the adulterer and adulteress mercy and forgiveness, the offended spouse may not likely be so understanding.
[Mentions of adulteress in the Bible.]