Charles H. Spurgeon on Psalms 135:3

Sing praises unto his name; for it is pleasant. The work of praising God hath a sort of reward joined with it. When we praise God most we get much benefit by so doing: it is so comely in itself, so pleasant unto God, and profitable to the person that offereth praises, so fit to cheer up his spirit, and strengthen his faith in God, whose praises are the pillars of the believer's confidence and comfort, that a man should be allured thereunto: "Sing praises unto his name; for it is pleasant; "and this is the second motive or reason to praise God the first being that "the Lord is good". —David Dickson.