John Calvin Commentary Psalms 124:4

"Then the waters had overwhelmed us, The stream had gone over our soul;" — Psalms 124:4 (ASV)

The waters had then overwhelmed us. He embellishes the preceding sentiment with an elegant metaphor, comparing the dreadful impetuosity of the enemies of the Jews to an inundation that swallows up whatever it meets in its overflowing course. And he continues to preserve the character of a frightened man.

He names the waters, next the torrent, and thirdly, the proud or impetuous waters. He says, over us, and over our soul, as if, by presenting the thing to the eye, he intended to strike terror into the people. And certainly, this impassioned language should have all the effect of a graphic representation, so that the faithful might better feel from what a profound gulf they had been rescued by the hand of God.

Only the one who acknowledges himself to have been lost before he was delivered truly attributes his deliverance to God. The adverb them is here either demonstrative, as if the Psalmist had pointed to the thing with his finger, or it means long ago. The former meaning, however, is more suitable to the present passage.