John Calvin Commentary Psalms 73:9

"They have set their mouth in the heavens, And their tongue walketh through the earth." — Psalms 73:9 (ASV)

They have set their mouth against the heavens. Here it is declared that they utter their insolent speeches against God as well as against men, for they imagine that nothing is too difficult for them to attempt, and flatter themselves that heaven and earth are subject to them. If anyone should try to alarm them by setting the power of God before them, they boldly break through this barrier; and, with respect to men, they have no idea of any difficulty arising from that source. Thus, there is no obstacle to restrain their proud and boasting speeches, but their tongue walketh through the whole earth. This form of expression seems to be exaggerated; but when we consider how great and unbounded their presumption is, we will admit that the Psalmist teaches nothing but what experience shows to be matter of fact.