Adam Clarke on Psalms 117:2

For his merciful kindness is great - גבר gabar, is strong: it is not only great in bulk or number, but it is powerful; it prevails over sin, Satan, death, and hell.

And the truth of the Lord endureth for ever - Whatsoever he has promised, that he will most infallibly fulfill. He has promised to send his Son into the world, and thus he has done. He his promised that he should die for transgressors, and this he did. He has promised to receive all who come unto him through Christ Jesus, and this he invariably does. He has promised that his Gospel shall be preached in every nation, and this he is doing; the truth of the Lord remaineth for ever. Therefore, Praise ye the Lord!