Monk Moses of Mount Athos: The Mature Fruit of Prayer

The power of prayer is to be found in its mature fruit, increasingly savored by the believer as he persists in long struggle. 
Abba Neilos says that prayer is protection against sadness and discouragement, which means that prayer protects the soul from the sins of dispirited sadness, despondency, oppression and despair.  And he adds: "It is prayer which blossoms the spirit of meekness and peacefulness."  These virtues are fruits of prayer, not acquired by momentary action, but requiring continuous fervent effort.
The most discerning St. John of the Ladder refers to prayer as the source of virtues, the nourishment of the soul, the enlightenment of the mind, the weapon which cuts off despair, the overcoming of grief, the reduction of wrath, the mirror of progress, the indicator of moderation, and the true reflection of our spiritual condition.

From Athonite Flowers: Seven Contemporary Essays on the Spiritual Life