Albert Barnes Commentary Psalms 136:1

"Oh give thanks unto Jehovah; for he is good; For his lovingkindness [endureth] for ever." — Psalms 136:1 (ASV)

O give thanks unto the Lord, for he is good - This whole verse is the same as Psalms 106:1, except that it is introduced by a Hallelujah. See the notes at that verse.

For his mercy endureth for ever - See also Psalms 106:1, note; Psalms 107:1, note. Literally, “For to eternity his mercy.” That is, it is ever the same; it never changes; it is never exhausted; it is found in all his dealings - in all his acts toward his creatures, and ever will be.