What is the purpose of this Mizmor?
Malbim: It founds a wondrous foundation of Emunah.
How do we understand blessing Hashem?
Radak: When Hashem commands Brachah to You, also you should bless Him in your praises, everyone according to his intellect.
Malbim: The supreme source, its water never ceases. It is blessed and increased via deeds of lower beings. Hashem influences good to the good and those prepared for it. When the generation is not proper to receive it, the spring is sullied, the source is ruined and the conduits of influence do not give out their Brachah. This is the Brachah that Yisrael bless Hashem; via their good deeds and Tefilos, they fill the supreme pool, Hashem's river full of water of Chesed and mercy, and it empties onto the land. When their deeds are bad, the water sources and the river dry up. Chazal said, Yisrael add strength to the Gevurah above. The Brachah is a 'need' of above, to make flow the springs above and below, via good deeds.
Malbim (3): You give to Him strength and ability to bless you. This depends on your deeds.
Who are "Kol Avdei Hashem"?
Radak: They are the Chachamim and Chasidim who rise from their beds at night, and come to pray in Beis Hashem and thank His name.
Malbim: They are like faithful servants who serve day and night, and do not leave their assignments for a moment.
