From the additional notes to Charles Spurgeon's The Treasury of David, Psalm 119.
Verse. 58. — According to thy word. The Word of God may be divided into three parts; into commandments, threatenings, and promises; and though a Christian must not neglect the commanding and threatening word, yet if ever he would make the Word a channel for Divine comfort, he must study the promising word; for the promises are a Christian's magna carta for heaven. All comfort must be built upon a Scripture promise, else it is presumption, not true comfort. The promises are pabulum fidei, et anima fidei, the food of faith, and the soul of faith. As faith is the life of a Christian, so the promises are the life of faith: faith is a dead faith if it hath no promise to quicken it. As the promises are of no use without faith to apply them, so faith is of no use without a promise to lay hold on. — Edmund Calamy.