These two – the Spirit’s power and direction – correspond to two ways that the Word of God functions in our prayer. The power of the Spirit is offered in promises of God’s Word, and we experience it by faith in the promise. The direction of the Spirit is embodied in the wisdom of God’s Word, and we experience it by being saturated with that wisdom. So if we would “pray in the Holy Spirit” we should, like Mueller, pray the Word of God, trusting the promises and absorbing the wisdom.
– Piper, John; When I Don’t Desire God: How to Fight for Joy; Crossway; Wheaton, Ill.; copyright 2004; p. 167