Complete Commentary on the Whole Bible, by Matthew Henry, at sacred-texts.com
(Psa 135:1-4) God to be praised for his mercy.
(Psa 135:5-14) For his power and judgments.
(Psa 135:15-21) The vanity of idols.
The subject-matter of praise, is the blessings of grace flowing from the everlasting love of God. The name of God as a covenant God and Father in Christ, blessing us with all spiritual blessings in him, is to be loved and praised. The Lord chose a people to himself, that they might be unto him for a name and a praise. If they do not praise him for this distinguishing favour, they are the most unworthy and ungrateful of all people.
God is, and will be always, the same to his church, a gracious, faithful, wonder-working God. And his church is, and will be, the same to him, a thankful, praising people: thus his name endures for ever. He will return in ways of mercy to them, and will delight to do them good.
These verses arm believers against idolatry and all false worship, by showing what sort of gods the heathen worshipped. And the more deplorable the condition of the Gentile nations that worship idols, the more are we to be thankful that we know better. Let us pity, and pray for, and seek to benefit benighted heathens and deluded sinners. Let us endeavour to glorify his name, and recommend his truth, not only with our lips, but by holy lives, copying the example of Christ's goodness and truth.