When peace of heart is a problem

A brother said to an old man, “I see no warfare in my heart.”  The old man said to him, “You are a building open on all sides, and whoever wishes can pass through you and you are unaware of it.  If you have a door, you should shut it, and not allow evil thoughts to enter through it; for then you will see them standing outside, banging on the door, and attacking you.”

— From the Sayings of the Desert Fathers