The answer
St. Augustine says, “And so that he might more dearly indicate the interior mouth which he signified by those words when he said: ‘Set a watch, O Lord, before my mouth, and a door of continence round about my lips,’ he immediately added: ‘Incline not my heart to evil words’ (Ps. 141:4). This inclination of the heart, what is it if not consent? For, he has not yet spoken who has not yet consented by an inclination of the heart to the onrushing suggestions in his heart of any aspect whatever. If, however, he consented, he has already spoken in his heart even though he has not made a sound with his mouth … ‘For out of the heart,’ He says, ‘come evil thoughts, murders, adulteries, immorality, thefts, false witnesses, blasphemies. There are the things that defile a man’ (Matt. 15:19–20).”812
Fr. Tadros Yacoub Malaty
Notes
812 St. Augustine of Hippo, On Continence 2.3–4 (FOTC 16:190–192).