John Calvin Commentary 2 Corinthians 3:5

"not that we are sufficient of ourselves, to account anything as from ourselves; but our sufficiency is from God;" — 2 Corinthians 3:5 (ASV)

Not that we are competent. When he thus disclaims all merit, it is not as if he humbled himself in merely pretended modesty; rather, he speaks what he truly thinks. Now we see that he leaves man nothing. For the smallest part of a good work, in a way, is thought.

In other words, it has neither the first part of the praise nor the second; and yet he does not allow us even this. Since it is less to think than to will, how foolishly do those act who claim for themselves a good will, when Paul does not leave them even the power of thinking anything!

Papists have been misled by the term sufficiency, which is used by the Old Interpreter. For they think to evade the point by acknowledging that man is not qualified to form good purposes, while at the same time they ascribe to him a sound understanding, which, with some assistance from God, can achieve something by itself. Paul, on the other hand, declares that man lacks not merely sufficiency of himself (αὐτάρκειαν), but also competency (ἱκανότητα), which would be equivalent to idoneitas (fitness), if such a term were used by Latin writers. He could not, therefore, more effectually strip man bare of everything good.