How is john proctor forgetting the commandment ironic?

It is ironic that John Proctor forgets the commandment "Thou shalt not commit adultery" because he has committed adultery with Abigail Williams. This forgotten commandment is one of the Ten Commandments that God gave to Moses on Mount Sinai. It is a moral law that prohibits sexual relations between a married person and someone other than their spouse. By committing adultery, John Proctor has broken this commandment and has therefore sinned against God.