Attention is the first teacher of truth and consequently absolutely necessary. Attention rouses the soul to study itself and its longings, to learn their true character and repulse those that are unholy. Attention is the guardian angel of the intellect, always counseling it this : be attentive. Attention awakens the soul, rouses it from sleep... Attention examines every thought, every desire, every memory. Thoughts, desires, and memories are engendered by various causes, and often appear masked and with splendid garb, in order to deceive the inattentive intellect and enter into the soul and dominate it. Only attention can reveal their hidden form. Often their dissimulation is so perfect that the discernment of their true nature is very difficult and requires the greatest attention. One must remember the saving words of the Lord: "Be wakeful and pray that ye enter not into temptation." He who is wakeful does not enter into temptation, because he is vigilant and attentive.
St. Neκtarios of Pentapolis