The deep realization that Christ is our only hope has significant existential force for a lot of people in motivating Christian faith. It is interesting that there need be nothing irrational here. In fact, a clearly valid argument can be given:
- Apart from Christ there is no hope.
- There is hope.
- If there is hope but apart from x there is no hope, then there is hope with x.
- If there is hope with Christ, the central doctrines of Christianity are true.
- So, there is hope with Christ. (1-3)
- So, the central doctrines of Christianity are true. (4-5)
Clichéd as that sounds, premise (1) really is something that I come to realize more and more deeply the longer I live. (See also this book by one of my distinguished colleagues.) Premise (3) is some kind of "logical truth'. Premise (4) would, I think, take some defending. I think the central thought here is something like the idea that Christ is Lord, liar or lunatic, and in the latter two cases there is no hope with Christ.
Premise (2) is the crucial one. I suspect that accepting (2) in the relevant deep existential sense of "There is hope" usually, perhaps always, is a fruit of grace. There is darkness, but one sees that there is light shining in it even if one cannot identify the light.
One can perhaps, though this very rare, argue oneself by the light of natural reason into accepting that the central doctrines of Christianity are true. But without grace one cannot argue oneself into accepting the central doctrines of Christianity (it is one thing to think something is true and another to accept it; I think the latest theorem proved by my colleagues at the Mathematics Department is true, but I don't accept it—if only because I don't know what it is!), much less into having faith in them.
It may be that for some people the point where grace enters the process of gaining faith is precisely at premise (2). If grace enters the process at accpetance of (2), this is quite interesting. For (2) is not overtly Christian. Yet when someone comes to faith in this way, with grace entering the process in conjunction with an existentially rich acceptance of (2), it plausibly follows that at that stage they already have faith. For, plausibly, there is no way to get to faith from something that isn't faith without grace. So that means that a deep existential acceptance of (2) (and that's not just a light and breezy optimism) could itself be faith.
The reflections on grace and faith are simply speculation. But the argument I stand by.