James 3:9 [ASV] “Therewith bless we the Lord and Father; and therewith curse we men, who are made after the likeness of God:”

“…Therewith, or, by it, bless we God. It is a clear instance of its deadly poison, that it can thus through a monstrous levity 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 as to men, in whom his image and glory peculiarly shine forth. It is then a hypocrisy not to be borne, when man employs the same tongue in blessing God and in cursing men. There can be then no calling on God, and his praises must necessarily cease, where evil speaking prevails; for it is an impious profanation of God’s name, when the tongue is virulent towards our brethren and pretends to praise him. That we may therefore rightly praise God, the vice of evil-speaking as to our neighbour must especially be corrected.

This particular truth ought also to be borne in mind, that sever censors discover their own virulence, when they suddenly vomit forth against their brethren whatever curses they can imagine, after having in sweet strains offered praises to God. Were any one to object and say, that the image of God in human nature has been blotted out by the sin of Adam; we must, indeed, confess that it has been miserably deformed, but in such a way that some of its lineaments still appear. Righteousness and rectitude, and the freedom of choosing what is good, have been lost; but many excellent endowments, by which we excel the brutes, still remain. He, then, who truly worships and honours God, will be afraid to speak slanderously of man.” Calvin’s Commentary on James 3:9