Sing, O ye heavens; for the LORD hath done it: shout, ye lower parts of the earth: break forth into singing, ye mountains, O forest, and every tree therein: for the LORD hath redeemed Jacob, and glorified himself in Israel.
Sing, O ye heavens - call to inanimate nature to praise God; because it also shall share in the coming deliverance from "the bondage of corruption" (Romans 7:20-21).
For the Lord hath done it - hath effected redemption for both the literal and spiritual Israel.
Shout, ye lower parts of the earth - antithetical to "heavens."
Mountains ... forest, and ... tree, are the intermediate objects in a descending gradation (see Psalms 96:11-12).