‘He who cultivates prayer has to fight with all diligence and watchfulness, all endurance, all struggle of soul and toil of body, so that he does not become sluggish and surrender himself to distraction of thought, to excessive sleep, to listlessness, debility and confusion, or defile himself with turbulent and indecent suggestions, yielding his mind to things of this kind, satisfied merely with standing or kneeling for a long time, while his intellect wanders far away.
For unless a person has been trained in strict vigilance, so that when attacked by a flood of useless thoughts he tests and sifts them all, yearning always for the Lord, he is readily seduced in many unseen ways by the devil.
Moreover, 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, this prayer – or, rather, this pretense of prayer – cannot profit us at all. And this applies not only to prayer, but to every labor and hardship undertaken for the sake of virtue, whether this be virginity, fasting, vigil, psalmody, service or any other work. If we do not see in ourselves the fruits of love, peace, joy, simplicity, humility, gentleness, guilelessness, faith, forbearance and kindliness, then we endure our hardship to no purpose. We accept the hardships in order to reap the fruits. If the fruits of love are not in us, our labor is useless.’
St. Symeon Metaphrastis
Wisdom and prayers of saints 