Let the floods clap their hands - The rivers. Let them join in the universal praise. As if conscious of their beauty, their grandeur, their usefulness; as if sensible that all this was conferred by God; as if rejoicing in the goodness of God manifested to them, and through them, let them unite in the universal praise. Compare the notes at Isaiah 55:12.
Let the hills be joyful together - The mountains - in view of the goodness of God toward them - crowning them with beauty - clothing them with sublimity and grandeur - let them also rejoice in God as "their" God. Let all nature thus join in praise.

Let the floods clap their hands - נהרות neharoth, properly the rivers - possibly meaning immense continents, where only large rivers are found; thus including inland people, as well as maritime stations, and those on the sea-coasts generally; as in those early times little more than the coasts of the sea were known. The Gospel shall be preached in the most secluded nations of the world.
Let the hills be joyful - All the inhabitants of rocky and mountainous countries.

Let the floods clap their hands,.... Or "rivers" (e), dashing against their banks, as they pass along; a prosopopoeia, as the preceding and following, expressing great joy on account of the Messiah, the reigning King. Aben Ezra interprets this of men that are in rivers, as the sea; in the preceding verse of such that are in ships at sea; and the hills in the next clause of such that dwell on them;
let the hills be joyful together; see Isaiah 55:12.
(e) "fluvii", Cocceius, Gejerus, so Ainsworth.