A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
psa 148:1The scope of this Psalm is the same as that of the preceding. (Psa 148:1-14)
heavens [and] heights--are synonymous.
psa 148:2hosts--(compare Psa 103:21).
psa 148:4heavens of heavens--the very highest.
waters--clouds, resting above the visible heavens (compare Gen 1:7).
psa 148:5praise the name--as representing His perfections.
he commanded--"He" is emphatic, ascribing creation to God alone.
psa 148:6The perpetuity of the frame of nature is, of course, subject to Him who formed it.
a decree . . . pass--His ordinances respecting them shall not change (Jer 36:31), or perish (Job 34:20; Psa 37:36).
psa 148:7The call on the earth, as opposed to heaven, includes seas or depths, whose inhabitants the dragon, as one of the largest (on leviathan, see on Psa 104:26), is selected to represent. The most destructive and ungovernable agents of inanimate nature are introduced.
psa 148:8fulfilling his word--or, law, may be understood of each. Next the most distinguished productions of the vegetable world.
psa 148:9fruitful trees--or, "trees of fruit," as opposed to forest trees. Wild and domestic, large and small animals are comprehended.
psa 148:11Next all rational beings, from the highest in rank to little children.
princes--or, military leaders.
psa 148:13Let them--all mentioned.
excellent--or, exalted (Isa 12:4).
his glory--majesty (Psa 45:3).
above the earth and heaven--Their united splendors fail to match His.
psa 148:14exalteth the horn--established power (Psa 75:5-6).
praise of--or literally, "for"
his saints--that is, occasions for them to praise Him. They are further described as "His people," and "near unto Him," sustaining by covenanted care a peculiarly intimate relation.