I sometimes wonder if there is any more vital lesson for Christian living than this: that God has condescended to our weakness by making us promises, that he will never break them, and that faith reckons on his faithfulness by grasping hold of them. We sometimes smile at the Victorians' 'promise-boxes'. Biblical promises were printed on small pieces of paper, rolled up like miniature scrolls and stored in a wooden box for random selection in times of need. And, to be sure, that practice did wrench the divine promises from the context in which they were originally given. Nevertheless, I rather think that even such a naive trust in detached promises was better than the present-day accurate but unbelieving knowledge of the promises in their context. So many of us complain of spiritual doubt, darkness, depression and lethargy, of besetting sins and unconquered temptations, of slow progress towards Christian maturity, of sluggishness in worship and in prayer, and of many other spiritual ills, while all the time we do not use the secret weapon which God has put into our hands.
--From "Life in Christ" (Eastbourne: Kingsway; Wheaton: Tyndale House, 1991), p. 27. Thanks JRW Stott.