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 98:1In view of the wonders of grace and righteousness displayed in God's salvation, the whole creation is invited to unite in praise. (Psa 98:1-9)
gotten . . . victory--literally, "made salvation," enabled Him to save His people.
right hand, and . . . arm--denote power.
holy arm--or, "arm of holiness," the power of His united moral perfections (Psa 22:3; Psa 32:11).
psa 98:2salvation--the result of His righteousness (Psa 7:17; Psa 31:1), and both are publicly displayed.
psa 98:3The union of mercy and truth (Psa 57:3; Psa 85:10) secure the blessings of the promise (Gen 12:3; Gen 18:18) to all the world (Isa 52:10).
psa 98:4make a loud noise--or, "burst forth" (Isa 14:7; Isa 44:23).
before . . . King--hail Him as your sovereign; and while, with every aid to demonstrate zeal and joy, intelligent creatures are invited to praise, as in Psa 96:11-13, inanimate nature is also summoned to honor Him who triumphs and rules in righteousness and equity.