God reigns from heaven as King over all. His authority extends to every created thing.
"The central theme of the book of Psalms, which its prayers assume and its songs of praise affirm, is God's kingship. . . .
"The book's theological message may be summarized as follows: As the Creator of all things, God exercises sovereign authority over the natural order, the nations, and Israel, His unique people. In His role as universal King God assures order and justice in the world and among His people, often by exhibiting His power as an invincible warrior. The proper response to this sovereign King is trust and praise."167
In view of His beneficent character all creatures should bless Him. This includes his powerful angelic servants (cf. Heb. 1:14) and all His creation. David ended this psalm as he began it by exhorting himself to bless the Lord.
This great psalm glorifies God by expounding His character. It teaches us what God is like. We should join the rest of creation in praising God because of who He is.