A great summary article on defining heresy from Amy Spreeman at the Berean Research blog, including a list of classic heresies that are well and truly thriving in the visible church and cults today:
So what constitutes a heresy? There’s no better resource than what CARM (Christian Apologetics & Resource Ministry) has put together on the subject. At the bottom of this article is a list of heresies determined by church councils throughout the centuries, with links and explanations:
“Heresy is a belief or idea that is in contradiction to orthodoxy. In the context of Christianity, heresy is that which deviates from standard biblical teaching. Examples of heresy would be polytheism, a denial of the resurrection of Christ, a teaching that salvation is obtained by works, etc. The Christian church has experienced many attacks by heretics throughout the centuries, but it has fought them successfully – even though many persist. There are modern-day heresies. For example, Mormonism which teaches God is an exalted man from another planet and that we can become gods. The Jehovah’s Witnesses deny the Trinity, deny the deity of Christ, and deny salvation by grace alone through faith alone. Roman Catholicism also and works to salvation and promotes Mary worship.
“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 on 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).
Read the rest of the article here.