John Calvin Commentary Psalms 50:7

"Hear, O my people, and I will speak; O Israel, and I will testify unto thee: I am God, [even] thy God." — Psalms 50:7 (ASV)

Hear, O my people! and I will speak. Until now, the prophet has spoken as the herald of God, employing several expressions designed to alarm the minds of those he addressed. But from this point to the end of the psalm, God himself is introduced as the speaker. To show the importance of the subject, he uses additional terms to awaken attention. He calls them his own people, that he might assert the greater authority of his words, and intimates that the following address is not merely ordinary but an expostulation with them for the infraction of his covenant.

Some read, I will testify against thee. But the reference, as we may gather from the common usage of Scripture, seems rather to be to a discussion of mutual claims. God would remind them of his covenant and solemnly exact from them, as his chosen people, what was due according to its terms. He announces himself to be the God of Israel, so that he may recall them to allegiance and subjection. The repetition of his name is emphatic: as if he had said, 'When you would have me submit to your inventions, how far is this audacity from the honor and reverence that belong to me?' I am God. Therefore, my majesty ought to repress presumption and make all flesh keep silence when I speak. And among you, to whom I have made myself known as your God, I have still stronger claims to homage.