Albert Barnes Commentary Psalms 115:2

"Wherefore should the nations say, Where is now their God?" — Psalms 115:2 (ASV)

Wherefore should the heathen say - The nations; those who worshipped idols, and who claimed that those idols were true gods. Why should we, your people, be so left, so forsaken, so afflicted, as to lead these idolaters to suppose that we worship a false God, or that the God whom we adore is destitute of power or faithfulness; either that he does not exist, or that he cannot be relied on? It is evident that they were now in circumstances which would give some plausibility to the question here asked.

Where is now their God? - They seem to be forsaken. God, the God whom they worship, does not come forth for their defense. If he exists at all, he is destitute of power, or he is not true to the people who worship him, and he cannot be trusted. Compare Psalm 42:3, note; Psalms 42:10, note; Psalms 79:10, note.