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 115:1The Psalmist prays that God would vindicate His glory, which is contrasted with the vanity of idols, while the folly of their worshippers is contrasted with the trust of God's people, who are encouraged to its exercise and to unite in the praise which it occasions. (Psa. 115:1-18)
The vindication of God's mercy and faithfulness (Psa 25:10; Psa 36:6) is the "glory" of His "name," which is desired to be illustrated in the deliverance of His people, as the implied mode of its manifestation. In view of the taunts of the heathen, faith in His dominion as enthroned in the heaven (Psa 2:4; Psa 11:4) is avowed.
psa 115:2Where is now, &c.--"now" is "not a particle of time, but of entreaty," as in our forms of speech, "Come now," "See now," &c.
psa 115:4(Compare Isa 40:18-20; Isa 44:9-20).
psa 115:7speak . . . throat--literally, "mutter," not even utter articulate sounds.
psa 115:8every one that trusteth--they who trust, whether makers or not.
psa 115:9The repetitions imply earnestness.
psa 115:14Opposed to the decrease pending and during the captivity.
psa 115:15They were not only God's peculiar people, but as living inhabitants of earth, assigned the work of His praise as monuments of divine power, wisdom, and goodness.
psa 115:18Hence let us fulfil the purpose of our creation, and evermore show forth His praise.