Matthew Henry on Psalms 115:1-8

Let no opinion of our own merits have any place in our prayers or in our praises. All the good we do, is done by the power of his grace; and all the good we have, is the gift of his mere mercy, and he must have all the praise. Are we in pursuit of any mercy, and wrestling with God for it, we must take encouragement in prayer from God only. Lord, do so for us; not that we may have the credit and comfort of it, but that they mercy and truth may have the glory of it. The heathen gods are senseless things. They are the works of men's hands: the painter, the carver, the statuary, can put no life into them, therefore no sense. The psalmist hence shows the folly of the worshippers of idols.