John Calvin Commentary Psalms 77:16

"The waters saw thee, O God; The waters saw thee, they were afraid: The depths also trembled." — Psalms 77:16 (ASV)

The waters saw thee, O God! Some of the miracles in which God displayed the power of his arm are briefly referred to here. When it is said that the waters saw God, the language is figurative, implying that they were moved, so to speak, by a secret instinct and impulse to obey the divine command in opening up a passage for the chosen people.

Neither the sea nor the Jordan would have altered their nature and, by making way, spontaneously provided a passage for them, had they not both felt the power of God upon them. It is not meant that they drew back because of any judgment and understanding which they possessed, but that in their receding, God showed that even the inanimate elements are ready to yield obedience to him.

There is an indirect contrast here, intended to rebuke the spiritual dullness of people if they do not acknowledge in the redemption of the Israelites from Egypt the presence and hand of God, which were seen even by the waters. What is added concerning the deeps implies that not only was the surface of the waters agitated at the sight of God, but also that his power penetrated even to the deepest gulfs.