Researching Religious Figures

In my Internet wanderings this week, I ran across a good essay about the psycho-historical/psycho-biographical study of religious personalities. The subject is of interest to me in two respects: (1) the methodologies involved in investigating an historical religious figure (as opposed to any other kind of historical person), and (2) issues related to understanding the interplay between psychology and spiritualism and/or religion. I am interested in questions like: What is the role of the researcher in studying religious subjects? What place does psychology – of both the researcher and the researched – have in such endeavors? How does one methodically and objectively research religious/spiritual experience? Etc.