John Calvin on 2 Corinthians 3:4

4. And such confidence As it was a magnificent commendation, that Paul had pronounced to the honor of himself and his Apostleship, lest he should seem to speak of himself more confidently than was befitting, he transfers the entire glory to God, from whom he acknowledges that he has received everything that he has. “By this boasting,” says he, “I extol God rather than myself, by whose grace I am what I am.” (1 Corinthians 15:10.) He adds, as he is accustomed to do by Christ, because he is, as it were, the channel, through which all God’s benefits flow forth to us.