From an e-mail by Kristor:
Comparative religion is useful to me in that it helps me limn the Religion of Adam, the religion naturally proper to natural man, which I take (and the Fathers took) to be Christianity.
The key thing is this.
If as a scholar of religion you approach Christianity as but one errant creature among many, as rather a taxonomist than a metaphysician, then you are on the road to Hell, or at least to nowhere (is there a difference between nowhere and Hell?)...
But if on the other hand you approach other religions as defective/partly successful & right approximations of the True Religion you are trying to discover and comprehend and practice, as rather a metaphysician than a taxonomist,
...why then you are almost bound in the course of your studies to arrive at the conclusion that orthodoxy – traditional Christianity, of whatever lobe of whatever “lung” – is the historical instantiation of that True Religion, and is thus the True Church...
(understanding the Church as extending throughout the cosmos (and indeed beyond it),
...and thus ipso facto throughout all human history, so that Christianity simply must be present incipiently in shamanism and animism, and in high paganism of the Neo-Platonist/Pythagorean sort, as in high Hebrew polytheism (El & His Son YHWH plus his pantheon of angels);
...and so that it is present at least partially in any religion that succeeds at informing a virtuous life of true human flourishing, or at fostering wisdom (however “merely” practical that wisdom).