From the inside, that is from the heart come all our sins. For Christ has said to the Apostles: “Not that which goeth into the mouth defileth a man” because it would mean to wash your hands “but that which cometh out of the mouth”. Because what comes out, comes from the heart. From the heart come adulteries, crimes, pride, insults. As in hell, they come out of our heart, and when they do, we are tempted from the inside.
When people restrain themselves from food but are gossiping and envy someone, it is considered a sin. What is the use of the bodily fasting if we ignore the spiritual fasting? What is the use of helping others if we amass fortune by stealing? What is the use of good deeds if we are proud? We are mixing good deeds with vainglory. The devil wins again. Even if we make good deeds, it is useless, because we are mixing them with evil.
According to Father Porphyries all these thoughts that come into our mind while praying are like planes. First, you can hear them in the distance, as a background noise, and gradually the noise increases more and more, until they get above your head deafening you with their noise and then they move forward. If you pay attention to them, then they will land in your heart.