John Gill Commentary Psalms 118:1

"Oh give thanks unto Jehovah; for he is good; For his lovingkindness [endureth] for ever." — Psalms 118:1 (ASV)

O give thanks unto the Lord
For all his mercies, temporal and spiritual; as all should, who are partakers of them: this should be done always, and for all things, in the name of Christ; it is but reasonable service;

for [he is] good ;
in himself, and to others: is essentially and diffusively good; the fountain of all goodness, and the author of all good things;

because his mercy [endureth] for ever ;
in his own heart, and in his covenant; his grace and lovingkindness displayed in Christ; the blessings and promises of it, which are the sure mercies of David: these always remain, notwithstanding the unworthiness of his people; and though he hides his face sometimes from them, and chastises them; see (Psalms 106:1) (107:1) ; the goodness and mercy of God were seen in setting David on the throne; and abundantly more in giving Christ to be the Saviour of his people; for both which thanks should be given, and the kindness acknowledged, by the persons mentioned in the following verses.