“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).
The word “heresy” comes from the Greek ‘hairesis’ which means “choosing” or “faction.” At first, the term heresy did not carry the negative meaning it does now. But, as the early church grew in its scope and influence throughout the Mediterranean area, various teachers proposed controversial ideas about Christ, God, salvation, and other biblical themes. It became necessary for the church to determine what was and was not true according to the Bible.
For example, 1) Arius of Alexandra (A.D. 320 ) taught that Jesus was a creation. Was this true? Was this important? Other errors arose.
2) The Docetists taught that Jesus wasn’t human.
3) The Modalists denied the Trinity.
4) The Gnostics denied the incarnation of Christ. Out of necessity, the church was then forced to deal with these heresies by proclaiming orthodoxy; and in so doing, condemnation upon these heresies and the heretics became a reality.