Albert Barnes Commentary Psalms 81:7

"Thou calledst in trouble, and I delivered thee; I answered thee in the secret place of thunder; I proved thee at the waters of Meribah. Selah" — Psalms 81:7 (ASV)

You called in trouble—The people of Israel (Exodus 2:23; Exodus 3:9; Exodus 14:10).

And I delivered you—I brought the people out of Egypt.

I answered you in the secret place of thunder—That is, in the lonely, secluded, solemn place where the thunder rolled. These were the solitudes where there was no voice but the voice of thunder, and where it seemed to come from the deep recesses of the mountain gorges.

The allusion is undoubtedly to Sinai . The meaning is that he gave a response—a real reply—to their prayer amid the solemn scenes of Sinai. It was there he gave them his law, recognized them as his people, and entered into covenant with them.

I proved you—I tried you; I tested your fidelity.

At the waters of Meribah—Margin, as in Hebrew, strife. This was at Mount Horeb (Exodus 17:5–7). The trial—the proof—consisted in his bringing water from the rock, showing that he was God, that he was their God.