This distinction between faith and assurance had profound doctrinal and pastoral implications for the Puritans. To make justification dependent upon assurance would compel the believer to rely upon his own subjective condition rather than on the sufficiency of a triune God in the order of redemption. Such reliance is not only unsound doctrine, but also bears adverse pastoral effects. God does not require full and perfect faith, but sincere and “unfeigned” faith. Fulfillment of God’s promises depends on the matter received, Christ’s righteousness, and not upon the degree of assurance exercised in the receiving. If salvation depended on the full assurance of faith, John Downame observes, many would despair for then “the palsied hand of faith should not receive Christ.” Happily, salvation’s sureness does not rest on the believer’s sureness of his salvation, for “believers do not have the same assurance of grace and favor of God, nor do the same ones have it at all times.” Pastorally, it is critical to maintain that justifying faith and the experience of doubt often coexist.
– Joel Beeke
as quoted by Sproul, R.C.; Grace Unknown: The Heart of Reformed Theology; Baker Books; Grand Rapids, MI; copyright 1997; p. 206