The Desert Fathers On Prayer

He who persists ceaselessly in prayer must not disparage the man incapable of doing this, nor must the man who devotes himself to serving the needs of the community complain about those dedicated to prayer. For if the prayers and the service are offered in the spirit of simplicity and love for others, the superabundnce of those dedicated to prayer will make up for the insufficiency of those who serve and vice versa. 
~ St. Makarios of Egypt 

When we pray, let our aim be this mystery of deification. which shows us what we once were like, and what the self-emptying of the only begotten Son through the flesh has now made us. ~ St. Maximos the Cpnfessor

Virtues are formed by prayer. Prayer preserves temperance. Prayer suppresses anger. Prayer prevents emotions of pride and envy. Prayer draws into the soul the Holy Spirit, and raises man to Heaven.  ~Saint Ephraim of Syria

Stillness, prayer, love and self-control are a four-horsed chariot bearing the intellect to heaven.
~ St. Thalassios the Libyan

If you are seated and see that prayer is active in your  heart, do not abandon it and rise for psalmody until in God's good time it leaves you of its own accord. Abandoning the interior presence of God, you will address yourself to Him from without, thus passing from a higher to a lower state, provoking unrest and disrupting the intellects serenity ~St. Gregory of Sinai

Those not yet capable of persisting in prayer can easily grow arrogant, thus allowing the machinations of evil to destroy the good work in which they are engaged and making a present of it to the devil. Unless humility and love, simplicity and goodness regulate our prayer, the pretense of prayer cannot profit us. ~ St Markios of Egypt