Origen's Homily on Numbers

"For the Spirit of God rests on those 'who are pure in heart,' and on those who purify their souls from sin. But on the other hand he does not dwell in a body subject to sins, even if he may have once dwelt therein. For the Holy Spirit cannot suffer the company and fellowship of an evil spirit. For it is certain that an evil spirit is present in each one's heart at the moment of sin, and it plays its part. Assuredly when room is given to an evil spirit, and we receive it through evil thoughts and wicked lusts, the Holy Spirit, feeling grieved and having been, so to speak, crowded out, flees from us." Origen, Homily 6 Numbers 11:16-25; 12:1-15.