The Nag Hammadi codices were not discovered until 1945. Included among them was the complete Gospel of Thomas. I recommend that you read some of Princeton scholar Elaine Pagel's works ('The Gnostic Gospels,' or 'The Gnostic Paul'). I bought her last book this very day - 'Beyond Belief.'
The Church Fathers who edited the other Christian books out of the canon, now referred to as Apocryphal writings, were at something of a loss - a great loss - because all of the information was not available. The Gospel of John might not have made it into the canon because it is Gnostic in flavor, and the Revelations of John is only one of several apocalyptic pieces that the editors decided to include. Feeling wild and crazy that day I suppose.
Just because Paul talks down those so-called Gnostics who were 'puffed up' with a kind of Knowledge, which led some to the conclusion that once saved, one could be as libertarian as one wanted, does not condemn all of the movements referred to generally as Gnosticism. Pagel's Gnostic Paul shows line-by-line how Gnostic the Biblical Paul's words are. Some Gnostics rejected Paul, others embraced him utterly.
Just what constitutes heresy - for you - has been carefully honed and handed down, to all of us, by these very human Churchmen (not women, despite Clement of Alexandria's position that women could become priests). It was THEIR decisions that determined what writings YOU could consider to be the Word of God. Their misogynistic mentalities, unBiblical celibate priesthood ideals, and their political agendas for controlling the masses all entered into what ancient writings would henceforth be taken as Holy Writ. Now take the Protestant mentality back to the beginning, and protest if one will, that with much more information at one's modern disposal, every man of faith ought to be able to determine doctrine. And as Clement said, true Gnosis is not apart from one's faith experience.
As for me - I was predominantly a Johannine Christian until I discovered Thomas, and it is this Gospel that speaks to MY faith experience. It is the Gospel of Thomas that describes MY experience of Christ moreso than the other canonical books or Nag Hammadi writings. Thomas may indeed be the earliest fragments of an oral tradition that preceded even Mark's source. If I reserve the right to come to my own, free-willed decisions, based upon my own scholarship and conscience, I do not necessarily hold 'wrong views' (heresies), based on dated and incomplete early Christian scholarship. As Archbishop J.S. Spong titled one of his books: 'Christianity Must Change or Die.'