Vigilance and prayer should be as closely linked together as the body to the soul, for the one cannot stand without the other. Vigilance first 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.
~St Symeon the New Theologian
Prayerful Life 