A heresy is a teaching that deviates from the truth of Biblical revelation. It is a false teaching. The word comes from the Greek airesei, "heireseis." The word occurs 9 times in the New Testament and is translated as "sect" in Acts 5:17, 15:5, Acts 24:5, 24:14 (NASB), Acts 26:5, 28:22. It is translated as "heresy" in the KJV at Acts 24:14, 1 Cor. 11:19, Gal. 5:20, 2 Pet. 2:1. The word is translated as "factions" in the NASB at 1 Cor. 11:19, Gal. 5:20, and "heresies" in 2 Pet. 2:1.
We are warned against heresy in several verses:
- 1 Cor. 11:19, "For there must also be factions (heresies) among you, in order that those who are approved may have become evident among you."
- Acts 20:29-30, "I know that after my departure savage wolves will come in among you, not sparing the flock; 30 and from among your own selves men will arise, speaking perverse things, to draw away the disciples after them."
- Phil. 3:2, "Beware of the dogs, beware of the evil workers, beware of the false circumcision."
Heresies would include the denial of monotheism (Mormonism), the Trinity (Jehovah's Witnesses, Islam), the deity of Christ (JW, Islam), and the personhood of the Holy Spirit (Jehovah's Witnesses, Christadelphians, The Way International). Other heresies are the teachings that men may become gods (Mormonism), there is more than one God (Mormonism), Jesus lost His divinity in Hell and finished the atonement there, and good works are necessary for salvation (all cults say this), etc.
"Error, indeed, is never set forth in its naked deformity, lest, being thus exposed, it should at once be detected. But it is craftily decked out in an attractive dress, so as, by its outward form, to make it appear to the inexperienced (ridiculous as the expression may seem) more true than truth itself," (Irenaeus, Against Heresies 1.2).
The word, "heresy," originally meant "choose" or "faction," but as the early church grew, false teachers started to infiltrate. It became necessary for the early church to determine what was and was not true doctrine.
The Bible condemns false doctrines and false teachers. Gal. 1:8-9 says, "But even though we, or an angel from heaven, should preach to you a gospel contrary to that which we have preached to you, let him be accursed. 9 As we have said before, so I say again now, if any man is preaching to you a gospel contrary to that which you received, let him be accursed." See also 1 Cor. 16:22, 2 Cor. 11:13-15, 1 Tim. 1:18-20, Titus 3:10.
Christians are saved by faith in the work of Jesus on the cross, but faith by itself is not enough. Faith is not a substance you obtain. Faith is belief, and faith is only as good as whom you place it in. False gods don't save anyone. This is why the True God says in Exodus 20:3, "You shall have no other gods before Me." Faith is not what saves, but faith in the true God is what saves.