John Calvin Commentary James 3:9

"Therewith bless we the Lord and Father; and therewith curse we men, who are made after the likeness of God:" — James 3:9 (ASV)

With it, or, by it, we bless God. It is a clear example of its deadly poison, that it can, in this way, through a monstrous inconsistency, transform itself; for when it pretends to bless God, it immediately curses Him in His own image, even by cursing men. For since God ought to be blessed in all His works, He ought to be so especially concerning men, in whom His image and glory uniquely shine forth. It is then an unbearable hypocrisy when man uses the same tongue for blessing God and for cursing men. Then there can be no calling on God, and His praises must necessarily cease when evil-speaking prevails; for it is an impious profanation of God’s name when the tongue is hostile toward our fellow human beings and yet pretends to praise Him. Therefore, so that one may rightly praise God, the vice of evil-speaking about our neighbor must especially be corrected.

We should also keep in mind this particular truth: severe critics reveal their own hostility, which they suddenly spew out against their fellow human beings with whatever curses they can imagine, after having offered praises to God in sweet tones. If anyone were to object and say that the image of God in human nature has been erased by the sin of Adam, we must, indeed, confess that it has been miserably deformed, but in such a way that some of its features still appear. Righteousness, uprightness, and the freedom to choose what is good have been lost; but many excellent endowments, by which we surpass the animals, still remain. Therefore, whoever truly worships and honors God will be afraid to speak slanderously of man.