Hippolytus: The Refutation of All Heresies
Hippolytus continues tracing the relationship between the Gnostics and the mystery cults, and emphasizing the areas where they are deficient in their theology (to say it as generously as possible). He notes their tendency to over-spiritualize everything (this is especially true of those who worship the "Great Mother", magna mater):
They rashly assume in this manner, that whatsoever things have been said and done by all men, (may be made to harmonize) with their own particular mental view, alleging that all things become spiritual.One reason the various heresies end up over-spiritualizing is their tendency to take (admittedly accurate) attributes of God and apply them to us as human beings. For example, they take the way that God creates the world through the Word/Idea (Logos), and declare that in the same way our ideas about the material world impart and create spiritual meaning. "Employing this exemplar, (the heretics) seem to adroitly introduce their secret mysteries, which are delivered in silence."
We can see here an early version of the Word-Faith heresy, where if only you have the right ideas you can attune yourself properly to the world and so flourish.
One thing that seems to stand out is that Hippolytus treats the heretics according to their own words and beliefs, not according to stereotypes about them held by their theological enemies. He regularly quotes their words (even a hymn or two) and appeals to their teachings, being careful to distinguish between different sects and schisms and paying close attention to the finer points of doctrine. Of course, it is virtually impossible for us to confirm most of what he says, as this is our sole source for many of these minor movements (unless there's something in Nag Hammadi that I'm not aware of--entirely possible, as I'm no scholar of Gnosticism). But there at least appears to be a good model for us on how to engage with those who claim to be Christian but in fact are heretics. We should be careful, thorough, generous, and attentive to what they believe, and formulate our response accordingly.