Psalm 118:1

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.