There are three methods of prayer and attentiveness, by means of which the soul is either uplifted or cast down. Whoever employs these methods at the right time is uplifted, but whoever employs them foolishly and at the wrong time is cast down. Vigilance and prayer should be as closely linked together as the body to the soul, for the one cannot stand without the other. Vigilance fist goes on ahead like a scout and engages sin in combat. Prayer then follows afterwards, and instantly destroys and exterminates all the evil thoughts with which vigilance has already been battling, for attentiveness alone cannot exterminate them. This, then, is the gate of life and death. If by means of vigilance we keep prayer pure, we make progress; but if we leave prayer unguarded and permit it to be defiled, our efforts are null and void.
Since, then, as we said, there are three methods of attentiveness and prayer, we should explain the distinctive features of each, so that he who aspires to attain life and wishes to set to work may with firm assurance select what suits him best; otherwise through ignorance he may choose what is worse and forfeit what is better.
Excerpt from the Philokalia – The Three Methods of Prayer attributed to St. Symeon the New Theologian