Hippolytus: The Refutation of All Heresies
Like Tertullian, Hippolytus writes here against Marcion's dualistic view of the Bible. Where Tertullian highlights the errors within Marcion and the harmony of the two testaments of Scripture (Marcion's heresy was to divide the Old from the New, and to declare that the God of the OT was evil, while the God of the NT was good--being consistent in this belief involved even chopping up the NT so that it conformed to this scheme), Hippolytus points out that Marcion's teachings aren't really Christian at all. They are in fact lifted from the philosopher Empedocles and given Christian names. Instead of "Friendship" and "Discord," we get the God of the OT and the God of the NT.
Both Marcion and his student Prepon reject the salvation of Christ when the reject the Incarnation and human birth of our Savior, and in doing so show the true heart of their religion: disdain for the created order.
The heretic Carpocrates, on the other hand, doesn't even let the world be created by God--it was created by angels. Jesus was not Incarnate, He was born as all men are (Joseph was His father), but then was raised up by communion with God to become a God, and show the rest of us the way.
Cerinthus holds something similar, arguing that it was at His baptism that Jesus was selected by God to work miracles and preach. The Ebionaeans and Theodotus follow this teaching as well, though they at least admit that God is the creator of the world.
The Melchisedecians argue that Jesus just appeared to be God, but was not in reality. This seems to be similar to the teaching of the Nicolatians--here we get a bit of the background of Nicolaus, though this may or may not be accurate when set beside similar treatments in Tertullian, Irenaeus, and Eusebius.
But why are there so many heresies? While this chapter (like most of the book so far) really can be skimmed, be sure not to miss this observation, buried in the discussion of Carpocrates:
Now these heretics have themselves been sent forth by Satan, for the purpose of slandering before the Gentiles the divine name of the Church. And the devil's object is, that men hearing, now after one fashion and now after another, the doctrines of those heretics, and thinking that all of us are people of the same stamp, may turn away their ears from the preaching of the truth, or that they also, looking, without abjuring, upon all the tenets of those heretics, may speak hurtfully of us.