The man who does not humble himself and does not cleanse his heart from evil desires fasts in vain. He may eat nothing at all, but it will be to no avail if there is evil inside him. He must first cleanse himself from the evil within in order to receive the Lord.
When the enemy tempts you with thoughts of faithlessness, with all your heart say, I believe completely whatever the Church believes, whatever Christ says in the Holy Gospels, whatever the Holy Apostles and the Holy Fathers said. 'I don't, however, believe you, devil, for you are a liar and a thief.'