Musar zu Tehillim 51:12

We have previously discussed the fact that anyone whose soul, נשמה, is rooted in the very highest regions of the Celestial Spheres, in the עולם האצילות, can never be the cause of sin. If however, his soul is only on the level of רוח, then he may become the source of sin through the seduction of the serpent which was affected by the spirit of envy, which in turn brings in its wake the spirit of טומאה, impurity. King David constantly begged that the Holy Spirit, רוח הקדושה, as well as the spirit of wisdom and understanding may inhabit him, and that the prophecy of Zachariah 13,2, where G–d says "I will remove the spirit of impurity from Earth," be fulfilled in the future.

Purity is the rectification of the heart and the thoughts. We find this term used by king David who said: "Create in me a pure heart, O G-d" (Tehilim 51:12).

The way to attain this trait is easy for one who has already strove and attained all the aforementioned traits. For when one thinks and contemplates on the lowliness of the pleasures of this world and its good, as I wrote earlier, he will come to despise them, and will not consider them to be anything but evils and lackings of the dark and coarse physical nature. When the truth ingrains within him of their being real lackings and evils, certainly it will become easier for him to separate from them and remove them from his heart.