In response to a reader email, there are a few things to note about Rudolph Otto's The Idea of the Holy.
While Otto's conception of the sacred and our interaction with it intrigues me, there are, as I've mentioned, reasons to be wary of adopting Otto's theory in toto. I've alluded to the possible problems with Otto's idealization of total/partial obscurity being the hallmark of language in which the sacred is expressed. Others have noted Otto's conception of the sacred is grounded in specifically Western and particularly Christian thought. There's a good deal of substance to this criticism. Otto effuses over the quality of Christianity's expression of the sacred over and against all previous and subsequent religious formulations. Otto never distinguishes which Christianity he means: Jesus' original movement, the conception of Jesus held by his earliest followers, the sub-apostolic period, the early or late patristic period, the medievals, etc. Others have critiqued Otto for holding the a priori position that the sacred is, ultimately its own category, removed from cultural context. I'm less convinced by this argument, but it's important to know that it is out there.
The challenge, I suppose, when reading Otto is to identify his basic conceptualization, see if there is anything of use there or anything that particularly resonates with you, and disentangle it from his argumentation. This is similar, though not identical, to what Victor Turner did with liminality from the work of Van Gennep.