What makes prayer, prayer? This enriching ordinance of God brings the believer into great familiarity with God, opens God’s heart to us, and fills our empty souls. Prayer obtains great things from God and is the very friendship of the soul with God. But what is the heart of prayer? Is there an essence to prayer without which “all your lifting up, both of hands, and eyes, and voices, will be to no purpose at all”? Yes. And the God who hears prayer has left us plain instruction about the living essence, the beating heart, of prayer. John Bunyan finds the key in the Apostle Paul’s words: “I will pray with the spirit, and I will pray with the understanding also.” He begins with a memorable definition of prayer. Then he explores the two great aspects of the heart of prayer: prayer with the Spirit, and prayer with the understanding. May this sermon in booklet form bear the fruit of Spirit-empowered prayer for God’s glory and the joy of God’s people everywhere.