We’re committed to some things because of evidence and to other things out of vows. “Evidence” has a field of meanings just as “vow” is also part of a larger field including what is sacred, what we are faithful to, etc. Both commitments can be absolute, though not in the same way. The principle of contradiction, basic truths of the sciences, a shared life with my wife, and my willingness to kill or die for (at least a few) American interests are all things about which I’m not open to alternatives, but there is more than one kind of absolute commitment in play. I’m not in doubt about the PoC but I also can make no sense about what it would mean to die for it; and I’m not open to life with women other than my wife but this was not after a thorough vetting of all other alternatives or an analytic insight that showed her preferable to all others.
As Nietzsche noticed these two sorts of commitment coalesce in our commitment to truth, so much so that truth seems like an iridescent color that seems now evidential, now sacred. Without denying the evidence of things, N. would still insist that this evidence is also implicated in a will to truth. The Christian existentialists (I’m thinking of Blondel and Marcel) can be read as agreeing to the same thing, but then questioning the opposition between what is revealed and what is rational. The evidential and the sacred are too implicated in one another to be divided sharply as distinct logoi, which gives rise to a Christian philosophy, even if this idea is as obscure as Christian geometry.