Notes from Wikiquote
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' (Heb. 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 Cor. 12:6) | for there is a single action of Father, Son and Holy Spirit, activating all things through Christ Jesus. | #113, On Commandments and Doctrines, p. 237-8.