[polemikos]

Actually Calvinism was not a new doctrine at all. The approach was pretty similar to the theology of Augustine who lived about a thousand years earlier.

from a novice's perspective: isn't this an ad verecundiam error?

or is the author trying to say that Calvinism is virtually Catholicism?

[xzins]

or is the author trying to say that Calvinism is virtually Catholicism?

Nope. What they're saying is that deterministic, fatalistic Christianity is the same whether advocated by Augustine or Calvin. The catholic church has repudidated Augustine's determinist predestinism while keeping much of what he had to say on other subjects.