When an unclean spirit goes out of a person it roams through arid regions searching for rest, but finds none. Then it says, 'I will return to my home from which I came.' But upon return it finds it empty, swept clean, and put in order. Then it goes and brings back with itself seven other spirits more evil than itself, and they move in and dwell there; and the last condition of that person is worse than the first. (Mt 13:43-45)
This bit of teaching has always fascinated me, and I guess I've always given it a psychological interpretation. If we begin (or begin again!) to pursue the interior life seriously, there is often a little euphoria as we try to let go of sins and negative patterns. But if we keep at it, we will soon uncover the more awful demons that we were previously medicating ourselves against.