The following handout lists works of reference (primarily dictionaries and encyclopedias) only, by Christian tradition. Some of these (just for example
will give you a (longer or shorter) introductory overview. But most will be best suited to answering a specific question.
For this reason (and because your professor wants you to do real research!), you must not neglect the search for at least introductory material in the form of books (under Find Books, above).