One a Facebook page, a Calvinist wonders how Calvinism is gnosticism.
Main features of Gnosticism:
-A special elect with secret knowledge.
-An eternal hope in an ascension to a spiritual realm.
-God as Perfect Being theology… immutable and timeless.
-The material world is corruption and cannot be divine (see Calvinist conceptions of the Hypostatic Union).
God is Open 
Isn’t perfect Being theology from Platonism tough?
Yeah, gnosticism was very closely related to Platonism. Plotinus has disputes with them about the nature of the world. No parties involved would consider themselves not Platonists.
Is there an article available here or somewhere else that explains the differences and similarities? :-)