A beliefs rationality.. Isn't Christianity at odds with rationality and science at its core in some sense, and require a level of absurdness to make it faith?
No, I don't think so. I don't think that Christianity is true but that doesn't make it irrational or absurd. Of course there are plenty of people who believe it irrationally, but I think that's got more to do with their nature than with the nature of what it is they're believing. And of course there are forms of Christianity that are irrational or absurd, but not all of them. I don't think that a religion that has boasted some of the finest minds in history among its defenders can be intrinsically irrational or absurd.
I didn't say that the task of philosophy of religion is to evaluate
the belief's rationality though, I said that it is to evaluate the belief
rationally, which is wider and doesn't presuppose that the belief itself is rational. Although your misreading is interesting since
one of the tasks of philosophy of religion (especially in the last twenty years or so) has been to assess whether it is, or can be, rational to believe the claims of religion, and what it means for a belief (of any kind) to be rational in the first place.
About separating your theological/historical analysis from what you believe – You, more or less, wrote that it seemed unlikely that ”Christianity” would form spontaneously. Although, from a philosophical standpoint such occurrence wouldn't be unlikely, right?!
I'm not sure what you mean. I said that it seems unlikely that Christian beliefs could emerge independently of any influence from Christian tradition. For example, it seems unlikely that a society that had never had any contact with Christianity should believe that their sins are forgiven through the death on a cross of a man who was also God. The more specific a particular idea, the less likely it is to find it arising independently in different societies. That seems a reasonable view. So I don't know why you say it wouldn't be unlikely "from a philosophical standpoint". What do you mean by that?
Do you see past such historical or scientific ”likelyhoods”, or does your philosophical views adapt to fit your scientific knowledge when it comes to your personal beliefs?
I'm not sure if that makes enough sense, but I'd be happy for any answer.
I'm not sure it makes sense either but I'm happy to try to give an answer if you say more about what you mean! Of course a person's philosophical views do (or should) adapt to fit scientific knowledge. Philosophy and science are really the same thing - science is just philosophy done using certain methods that work in certain spheres, while what we call "philosophy" today is philosophy done in other spheres where strictly scientific methods don't work for one reason or another. So it would surely be irrational to have philosophical views that clash with science (unless of course one had philosophical reasons for mistrusting the claims of science, but those would have to be pretty impressive reasons).