Let us not be deceived by outward appearances. Satan “disguises himself as an angel of light” (2 Cor. 11:14). He keeps his deadliest diseases most sanitary. He clothes his captains in religious garments and houses his weapons in temples. Legalism is a more dangerous disease than alcoholism because it doesn't look like one. Alcoholism makes men fail; legalism helps them succeed in the world. Alcoholism makes men depend on the bottle; legalism makes them self-sufficient, depending on no one. Alcoholism destroys moral resolve; legalism gives it strength. Alcoholics don't feel welcome in the church; legalists love to hear their morality extolled in church.
John Piper