I have questioned and doubted Christianity in the past. But I earnestly sought answers; some were given to me, and with the others, I was given comfort and faith that even though I don't understand it, God is in complete control. But now, as far as the big things are concerned - Christ's deity, crucifixion resurrection, and slavation, I have no doubts whatsoever. I believe with all my heart.
I can even boil it down to a logical level. Logic and reason do play a role in my belief system. My knowledge is not limited to Christianity. I know quite a bit about many other religions. With every other monotheistic religion out there, a man's salvation depens on "how good he can be", "what he can do for God". Christianity takes that and stomps on it til it dies. In Christianity, man can't do a draned thing to "earn" God's acceptance, because man is sinful. Christ turns legalism on its ears - no matter what you do, you can't buy your way into his kingdom. Christ dies on teh cross to reconcile God and man. The other religions are all about "man reaching up to God". Christianity is all about "God reaching down to man, to lift him up - out of the mirey clay", to use the words of Bono. The way I see it, it makes more sense that if God is absolutely perfect and righteous, he cannot abide anything less than perfect and righteous. Therefore, the others don't cut it for me - they're exercises in futility. Christianity provided grace, and escape plan, that is based not on man's imperfect efforts but on the never failing love of God.