Likewise, I must agree with Frumanch that Calvinists do NOT believe they are "infused" with Christ's nature. As a a Protestant Christian I believe that we have an imputed righteousness, and never an infused righteousness. While various protestants disagree on many things, most do NOT disagree on that.
You continue to equate "once saved always saved" with "the perseverence of the saints." You are simply incorrect in thinking they are identical.
OSAS is a teaching that says you can do anything. POTS is a doctrine that says you will NOT do just about anything. It would be hard for 2 doctrines to be more different.
The intent was to show that salvation under the Gnostics and under the Calvinists are remarkably similar.
The nature of God is superimposed on the Calvinists and therefore they are saved. They have indwelling secret knowledge that has no outward signs. The mechanism is a secret and mystical one. Similarity.
Now, what about the rest of the heresies? Is this merely a smokescreen that furious debate about terms comparing Gnostic to Calvinist practices will obscure and hopefully leave behind the further comparison of Calvinistic and other 1st millennium heretical practices?