For beginners prayer is like a joyous fire kindled in the heart; for the perfect it is like a vigorous sweet-scented light. Or again, prayer is the preaching of the Apostles, an action of faith or, rather, faith itself, “that makes real for us the things for which we hope” (Hebrews 11:1), active love, angelic impulse, the power of the bodiless spirits, their work and delight, the Gospel of God, the heart’s assurance, hope of salvation, a sign of purity, a token of holiness, knowledge of God, baptism made manifest, purification in the water of regeneration, a pledge of the Holy Spirit, the exultation of Jesus, the soul’s delight, God’s mercy, a sign of reconciliation, the seal of Christ, a ray of the noetic sun, the heart’s dawn-star, the confirmation of the Christian faith, the disclosure of reconciliation with God, God’s grace, God’s wisdom or, rather, the origin of true and absolute Wisdom; the revelation of God, the work of monks, the life of hesychasts, the source of stillness, and expression of the angelic state. Why say more? Prayer is God, who accomplishes everything in everyone (cf. 1 Corinthians 12:6), for there is a single action of Father, Son and Holy Spirit, activating all things through Christ Jesus.
~St Gregory of Sinai