There is an interesting analogy brought in the ספר הישר describing how one needs to prepare himself to receive holiness, contentment, and peace of mind. There is a certain amount of cleaning that one must do.
The comparison is to a painter who must properly prepare the object he is painting. He must smooth out the surface and remove all obstructions, in order for the paint to be absorbed by the surface. If such preparations are not made, the paint will peel off in a short time.
The same holds true with our spirituality. If we don't drive away the חלאי המחשבה, the sick way of thinking in a negative way, and our unbridled lusts, the holiness will not take hold and will peel off in a short time.
Therefore, we must work on thinking positively and overcoming our desires. The reward will be our connection to Kedusha and Hashem.