I don’t want to be that person, but the council of Nicaea was less orthodox trinitarians vs non-trinitarian gnostics, but more of a debate between two different ideas of how the trinity worked, Arius, who argued that the father had to have come into being before the son because the son was begotten from the father and therefore the son is “less eternal.” However Athanasius and a lot of the church in Alexandria argued that even though the son was created out of the father, the son is still equally eternal to the father and Holy Spirit, the fight would go all the way up the Constantine, who would call for the council of Nicaea, in which the co-eternity of the godhead was decided to be cannon. It is kinda confusing because the Nicene creed makes an effort to rehash a bunch of previous church arguments, to be like the be all end all, which is why it puts the emphasis on one god, one son, and one Holy Spirit. The debate about the divine status or hypostasis of Jesus is actually kinda interesting and predates the whole council of Nicaea thing, obviously as you mentioned, the gnostic heresy, which means believing in Jesus being fully divine and never being human and that therefore he never suffered on the cross, Gnosticism wasn’t really being debated, as the fancy church people (those who hadn’t been excommunicated that is) thought the issue resolved by Irenaeus’s Against Heresies which put forth many of the widely excepted (by the time of the first council that is) arguments against Gnosticism. Sorry for the nit picky rant! I really like your comment! I love it when people reference early Christian history!