by St. Diadochos of Photiki
83. It is true that the heart produces good and bad thoughts from itself (cf. Luke 6:45). But it does this not because it is the heart's nature to produce evil ideas, but because as a result of the primal deception the remembrance of evil has become as it were a habit. It conceives most of its evil thoughts, however, as a result of the attacks of the demons. But we feel that all these evil thoughts arise from the heart, and for this reason some people have inferred that sin dwells in the intellect along with grace. That is why, in their view, the Lord said: 'But those things which proceed out of the mouth come forth from the heart; and they defile the man. For out of the heart proceed evil thoughts, adulteries', and so on (Matt. 15:18-19). They do not realize, however, that the intellect, being highly responsive, makes its own the thoughts suggested to it by the demons through the activity of the flesh; and, in a way we do not understand, the proclivity of the body accentuates this weakness of the soul because of the union between the two. The flesh delights endlessly in being flattered by deception, and it is because of this that the thoughts sown by the demons in the soul appear to come from the heart; and we do indeed make them our own when we consent to indulge in them. This was what the Lord was censuring in the text quoted above, as the words themselves make evident. Is it not clear that whoever indulges in the thoughts suggested to him by Satan's cunning and engraves them in his heart, produces them thereafter as the result of his own mental activity?