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 117:2This may be regarded as a doxology, suitable to be appended to any Psalm of similar character, and prophetical of the prevalence of God's grace in the world, in which aspect Paul quotes it (Rom 15:11; compare Psa 47:2; Psa 66:8). (Psa 117:1-2)
is great toward us--literally, "prevailed over" or "protected us."