Heresy always presents itself as an improvement on the biblical gospel. For the Colossians it promised to overcome their struggle with sin and bring them closer to God. For the Galatians it would keep them from persecution and fuel their desire to justify themselves before God by their works.
Heresy never appears in its true colours. In his monumental work Against Heresies Irenaeus wrote that “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 the truth itself.”