John Calvin on 1 Thessalonians 3:9

9 For what thanksgiving. Not satisfied with a simple affirmation, he intimates how extraordinary is the greatness of his joy, by asking himself what thanks he can render to God; for by speaking thus he declares that he cannot find an expression of gratitude that can come up to the measure of his joy. He says that he rejoices before God, that is, truly and without any pretense.