"Truly 'righteous' men and women of faith know the value of their heavenly Father's promises. They go to Him, as children do to a loving human father. They know that if they can say to an earthly father, 'But, father, you promised...,' they can both persist in asking and be confident that he will keep his word. How much more our heavenly Father, who has given His Son for our salvation! We have no other grounds of confidence that He hears our prayers. We need none.
"Such appeal to God's promises constitutes what John Calvin, following Turtullian, calls 'legitimate prayer.'
"Some Christians find this disappointing. It seems to remove the mystique from the prayer of faith. Are we not tying down our faith to ask only for what God already has promised? But such disappointment reveals a spiritual malaise: would we rather devise our own spirituality (preferably spectacular) than God's (frequently modest)?
"The struggles we sometimes experience in prayer, then, are often part of the process by which God gradually brings us to ask for only what He has promised to give. The struggle is not our wrestling to bring Him to give us what we desire, but our wrestling with His Word until we are illuminated and subdued by it, saying, 'Not my will, but Your will be done.' Then, as Calvin again says, we learn 'not to ask for more than God allows.'
"This is why true prayer can never be divorced from real holiness. The prayer of faith can be made only by the 'righteous' man whose life is being more and more aligned with the covenant grace and purposes of God. In the realm of prayer, too (since it is a microcosm of the whole of the Christian life), faith (prayer to the covenant Lord) without works (obedience to the covenant Lord) is dead."
From Sinclair Ferguson, In Christ Alone: Living the Gospel Centered Life (Orlando, FL: Reformation Trust), pp. 146-147.