Heresy: Denial of the Faith
Heresy is, at the most basic, any teaching or practice that denies the tenets of the Historic Christian Faith, causes sinful division, and is deserving of condemnation. Heresy should be taken very seriously but is often overlooked in the modern Church as we, especially in the West, have taken on a very pragmatic approach to the Faith.
Things that Divide
Unity in the essentials is vitally important to the health of the Body of Christ and should be sought after diligently, but there are times where the issues demand action.
The Church has dealt with these issues as they have arisen and many of the earliest heresies dealt with the Nature of Christ, the Trinity, and the nature of man. Among these issues are Arianism, Socinianism, Nestorianism, and Pelagianism: most of which have continued in one form another to the current day.
Other heresies include an attempt to reconcile Pelagianism with orthodoxy in the form of Semi-Pelagianism, The Word of Faith Movement, and Adoptionism.