Charles H. Spurgeon on Psalms 136:1

His mercy. Many sweet things are in the word of God, but the name of mercy is the sweetest word in all the Scriptures, which made David harp upon it twenty-six times in this Psalm: "For his mercy endureth for ever:" It was such a cheerful note in his ears when he struck upon mercy, that, like a bird that is taught to pipe, when he had sung it, he sang it again, and when he had sung it again, he recorded it again, and made it the burden of his song: "For his mercy endureth for ever." Like a nightingale which, when she is in a pleasant vein, quavers and capers, and trebles upon it, so did David upon his mercy: "For his mercy endureth for ever." —Henry Smith.