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 of 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).
A lifelong student of the Bible, Peter DeHaan, PhD, wrote the 700-page website ABibleADay.com to encourage people to explore the Bible. His main blog and numerous books urge Christians to push past the status quo and reconsider how they practice their faith in every area of their lives.