The word "deep" refers to deep waters, which here are likely the streams rushing down Mount Hermon. The writer speaks of them as if they are people calling out to one another as they hear the sound of their own descent from the mountain. (See: [[rc://en/ta/man/translate/figs-personification]])
The author speaks of his great misfortune and sadness as if they are deep waters that drown him with one wave after another. (See: [[rc://en/ta/man/translate/figs-metaphor]])
The word "billows" is another word for "waves." Together the two words emphasize the greatness of the waves. AT: "all of your great waves" (See: [[rc://en/ta/man/translate/figs-doublet]])
The writer speaks of Yahweh's covenant faithfulness as if it were a person whom he commands to be with him. The abstract noun "faithfulness" can be translated as an adjective. AT: "Yahweh will show me his covenant faithfulness in the daytime" or "Yahweh will show me in the daytime how faithful he is to his covenant" (See: [[rc://en/ta/man/translate/figs-metaphor]])
# his song
Possible meanings are 1) "the song that he gives me" or "the song about him"