1 In the first book, which immediately precedes this, exposing “knowledge falsely so called,” I showed you, my very dear friend, that the whole system devised, in many and opposite ways, by those who are of the school of Valentinus, was false and baseless. I also set forth the tenets of their predecessors, proving that they not only differed among themselves, but had long previously swerved from the truth itself. I further explained, with all diligence, the doctrine as well as practice of Marcus the magician, since he, too, belongs to these persons; and I carefully noticed the passages which they garble from the Scriptures, with the view of adapting them to their own fictions.
Moreover, I minutely narrated the manner in which, by means of numbers, and by the twenty-four letters of the alphabet, they boldly endeavour to establish [what they regard as] truth. I have also related how they think and teach that creation at large was formed after the image of their invisible Pleroma, and what they hold respecting the Demiurge, declaring at the same time the doctrine of Simon Magus of Samaria, their progenitor, and of all those who succeeded him. I mentioned, too, the multitude of those Gnostics who are sprung from him, and noticed the points of difference between them, their several doctrines, and the order of their succession, while I set forth all those heresies which have been originated by them.
I showed, moreover, that all these heretics, taking their rise from Simon, have introduced impious and irreligious doctrines into this life; and I explained the nature of their “redemption,” and their method of initiating those who are rendered “perfect,” along with their invocations and their mysteries. I proved also that there is one God, the Creator, and that He is not the fruit of any defect, nor is there anything either above Him, or after Him.2. In the present book, I shall establish those points which fit in with my design, so far as time permits, and overthrow, by means of lengthened treatment under distinct heads, their whole system; for which reason, since it is an exposure and subversion of their opinions, I have so entitled the composition of this work.
For it is fitting, by a plain revelation and overthrow of their conjunctions, to put an end to these hidden alliances, and to Bythus himself, and thus to obtain a demonstration that he never existed at any previous time, nor now has any existence.
Source: Adversus haereses (New Advent)