Charles H. Spurgeon on Psalms 118:1

His mercy endureth for ever. What the close of Psalm 117 says of God's truth, viz., that it endureth for ever, Ps 118:1-4 says of its sister, his mercy or lovingkindness. Franz Delitzsch.

Verses 1-4. As the salvation of the elect is one, and the love of God to them one, so should their song be one, as here four several times it is said, His mercy endureth for ever. David Dickson.

Verses 1-4. Because we hear the sentence so frequently repeated here, that "the mercy of the Lord endureth for ever, "we are not to think that the Holy Spirit has employed empty tautology, but our great necessity demands it: for in temptations and dangers the flesh begins to doubt of the mercy of God; therefore nothing should be so frequently impressed on the mind as this, that the mercy of God does not fail, that the Eternal Father wearies not in remitting our sins. Solomon Gesner.