This confirms what he had said in the close of the foregoing verses, All thy commandments are truth; he means the covenant, the word which God has commanded to a thousand generations. This is firm, as true as truth itself. For, 1. God has founded it so; he has framed it for a perpetuity. Such is the constitution of it, and so well ordered is it in all things, that it cannot but be sure. The promises are founded for ever, so that when heaven and earth shall have passed away every iota and tittle of the promise shall stand firm, Co2 1:20. 2. David had found it so, both by a work of God's grace upon his heart (begetting in him a full persuasion of the truth of God's word and enabling him to rely upon it with a full satisfaction) and by the works of his providence on his behalf, fulfilling the promise beyond what he expected. Thus he knew of old, from the days of his youth, ever since he began to look towards God, that the word of God is what one may venture one's all upon. This assurance was confirmed by the observations and experiences of his own life all along, and of others that had gone before him in the ways of God. All that ever dealt with God, and trusted in him will own that they have found him faithful.