“As St John of Damaskos says, without attentiveness and watchfulness of the intellect we cannot be saved and rescued from the devil, who walks about ‘like a roaring lion, seeking whom he may devour’ (1 Pet. 5:8). For this reason the Lord often said to His disciples, ‘Watch and pray; for you do not know at what hour your Lord is coming’ (Matt. 26:41, 24:42). Through them He was giving a warning to us all about the remembrance of death, so that we should be prepared to offer a defense, grounded in works and attentiveness, that will be acceptable to God. For the demons, as St Hilarion has said, are immaterial and sleepless, concerned only to fight against us and to destroy our souls through word, act and thought. We lack a similar persistence, and concern ourselves now with our comfort and with ephemeral opinion, now with worldly matters, now with a thousand and one other things. We are not in the least interested in examining our life, so that our intellect may develop the habit of so doing and may give attention to itself unremittingly.”
+ St. Peter of Damaskos, “Book I: A Treasury of Divine Knowledge,” The Philokalia: The Complete Text (Vol. 3)