If a professor had the persistent, disturbing, intrusive notions that there were germs lurking everywhere, on papers students handed in, on books checked out of the library, on the chalk left by the previous teacher, the professor would be experiencing

obsessive ideas

Explanation:

Obsessive ideas are characterized by uncontrolled thoughts of distressing thoughts and images which are usually accompanied by uneasy feeling and behavioral routines that seem reoccurring. The professor might start getting scared of falling ill or worry over little things such as papers that may contain germs. He may also indulge in compulsive behaviors that are obsessive, such as frequent washing of the hands.

because he was a christian?

the atm that sounds like it should be the answer