John Calvin Commentary Psalms 77:17

"The clouds poured out water; The skies sent out a sound: Thine arrows also went abroad." — Psalms 77:17 (ASV)

The clouds poured out waters. Since the noun מים, mayim, cannot be taken in the construct state, the verb, I have no doubt, is used transitively. However, it makes little difference to the meaning whether we take this view or read as if מים, mayim, were in the construct state and the verb passive—that is, whether we read, The clouds poured out waters, or, The waters of the clouds were poured out. The meaning is clearly that not only the sea and the river Jordan, but also the waters suspended in the clouds, yielded to God the honor to which he is entitled; the air, by the concussion of the thunder, poured forth copious showers.

The purpose is to show that, wherever people turn their eyes, the glory of God is illustriously manifested. This is true in every part of creation, above and beneath, from the height of heaven to the depths of the sea. What history is referred to here is somewhat uncertain.

Perhaps it is the event recorded in Exodus 9:23, where we are informed that hail mingled with thunder and lightning was one of the dreadful plagues inflicted upon the Egyptians. The arrows which went abroad are, no doubt, to be understood metaphorically as lightnings.

With this verse, we are to connect the following description, where it is said that the voice of the thunder was heard in the air, and that the lightnings illumined the world, so that the earth trembled. In essence, at the departure of the people from Egypt, ample testimony was given to the power of God, evident to both the eyes and ears of the people: peals of thunder were heard in every part of the heavens, and the whole sky shone with flashes of lightning, while at the same time the earth was made to tremble.