Biblical Commentary on the Old Testament, by Carl Friedrich Keil and Franz Delitzsh, [1857-78], at sacred-texts.com
Psalms Chapter 117
The thanksgiving Psalm ending in Hallelujah is followed by this shortest of all the Psalms, a Hallelujah addressed to the heathen world. In its very brevity it is one of the grandest witnesses of the might with which, in the midst of the Old Testament, the world-wide mission of the religion of revelation struck against or undermined the national limitation. It is stamped by the apostle in Rom 15:11 as a locus classicus for the fore-ordained (gnadenrathschlussmssig) participation of the heathen in the promised salvation of Israel.
Even this shortest Psalm has its peculiarities in point of language. אמּים (Aramaic אמיּא, Arabic umam) is otherwise alien to Old Testament Hebrew. The Old Testament Hebrew is acquainted only with אמּות as an appellation of Ismaelitish of Midianitish tribes. כּל־גּוים are, as in Psa 72:11, Psa 72:17, all peoples without distinction, and כּל־האמּים all nations without exception. The call is confirmed from the might of the mercy or loving-kindness of Jahve, which proves itself mighty over Israel, i.e., by its intensity and fulness superabundantly covering (גּבר as in Psa 103:11; cf. ὑπερεπερίσσευσε, Rom 5:20, ὑπερεπλεόνασε, Ti1 1:14) human sin and infirmity; and from His truth, by virtue of which history on into eternity ends in a verifying of His promises. Mercy and truth are the two divine powers which shall one day be perfectly developed and displayed in Israel, and going forth from Israel, shall conquer the world.