Prayer is by nature a dialogue and a union of man with God. Its effect is to hold the world together. It achieves a reconciliation with God.
Prayer is the mother and daughter of tears. It is an expiation of sin, a bridge across temptation, a bulwark against affliction. It wipes out conflict, is the work of angels, and is the nourishment of all bodiless beings. Prayer is future gladness, action without end, wellspring of virtues, source of grace, hidden progress, food of the soul, enlightenment of the mind, an axe against despair, hope demonstrated, sorrow done away with. It is wealth for monks, treasure of hermits, anger diminished. It is a mirror of progress, a demonstration of success, evidence of one’s condition, the future revealed, a sign of glory. For the man who really prays it is the court, the judgment hall, the tribunal of the Lord — and this prior to the judgment that is to come.
— St. John Climacus (ca. 579-649) Ladder of Divine Ascent, Step 28: On Prayer.