Albert Barnes Commentary Psalms 103:20

"Bless Jehovah, ye his angels, That are mighty in strength, that fulfil his word, Hearkening unto the voice of his word." — Psalms 103:20 (ASV)

Bless the Lord - The psalm began (Psalms 103:1–2) with an exhortation to “bless the Lord.” That exhortation, however, was then addressed by the psalmist to his own soul and was especially founded on the benefits he himself had received. The psalm also closes with an exhortation to “bless the Lord,” yet on a much wider scale. The psalmist feels that there is not only reason for him to do so, but that the reason for it extends to the whole universe.

The meaning is that God is worthy of universal praise, and all ranks of beings—all worlds—should join in that praise. Humankind, feeble, frail, and dying, could not attain the fullness of the praise required. Praise appropriate to God—such as His perfections and works deserved—demanded loftier powers than those of humans; the loftiest powers in the universe.

You His angels - All beings higher than humans; beings around and before His throne.

That excel in strength - Margin, as in Hebrew, “mighty in strength,” and therefore more “able” to offer adequate praise.

That do His commandments - Who perfectly obey His law, and who, therefore, can render more acceptable praise than can ever come from human lips.

Listening to the voice of His word - Who always listen to His voice; who never are disobedient; and who can, therefore, approach Him as holy beings, and more appropriately worship Him.