St. Maximos the Confessor: The demons attack the person who . . .

Icon of St. Maximos the ConfessorThe demons attack the person who has attained the summits of prayer in order to prevent his conceptual images of sensible things from being free from passion; they attack the gnostic so that he will dally with impassioned thoughts; and they attack the person who has not advanced beyond the practice of the virtues so as to persuade him to sin through his actions. They contend with all men by every possible means in order to separate them from God.

+ St. Maximos the Confessor, Four Hundred Texts on Love 2.90, The Philokalia: The Complete Text (Vol. 2)