Over on The Church of Jesus Christ we find a post on the usual populist tripe regarding the mystery schools and Christianity. While some cogent points are raised, I think the entire approach is endemic of the same problem.
I'm reminded of the cry of E P Sanders in Paul and Palestinian Judaism, for a comparison of religion that begins by first ensuring a solid understanding--in their own right--of the things being compared. With the exception of Smith's Drudgery Divine, I'm aware of no real inquiry into Christianity and any mystery cult that attempts to do this, and even Smith is, at times reactionary, and on the whole seems to me to have bitten off too much.
The problem, in the case of Smith, is that he discusses too many religions for the reader to really share an understanding of any of them. The problem, on The Church of Jesus Christ, is that it falls into the old trap of "yes it is"/"no it isn't." Which might help us catalogue some facts, but does nothing to further our understanding.
I'm certainly not about to suggest that I meet the description of the comparative scholar I long for, so instead I just wanted to touch a little bit on a cogent point raised: Namely the difficulty in telling which way syncretism might run.
In recent weeks I've spent some effort investigating the enigmatic rite known as the Taurobolium. It's frequent description as a "baptism in bull's blood" perhaps underscores the problems of comparison noted above, since in describing it as such we are "Christianizing" the ritual. A bibliography noting this phrasing would take far too long, but it's a conception of the ritual that makes it's way up to the highest level of academia, down to the outright layman who happened on the rite by chance. It's simply the description that best meets our post-Christian sentiments.
The "baptismal" form of the rite, as it's known to Prudentius in his Peristephanon, is in fact a quite late version, however. The earliest epigraphic attestation to the rite describes it as a sacrifice, frequently for the emperor or for the empire, a tendency that continued for quite some time. The cleansing or life-giving powers of the blood, with its 20 year efficacy, didn't appear until much later.
So, by indications of chronology and proximity, it is more likely Christianity that gave the bull's blood its powers, not the other way around, and while we should still avoid the term "baptism in bull's blood," there's a better than passing chance that it was the baptism of the exploding Christian movement that inspired the new interpretations. Certainly it is more plausible that the taurobolium was reinterpreted in the face of Christianity than it is that the taurobolium had had that significance all along, but nobody thought to mention it until centuries after.
Of course, in understanding the rite for its own sake, this just makes it all the more confusing. It was a sacrifice, but what, exactly, made it special? Differentiated it from other "bull-killings" such that it got it's own term? Clearly there was a concrete ritual involved, the full significance of which may be lost to us beyond conjectural speculation.