From The Reason for God by Timothy Keller:
Believers should acknowledge and wrestle with doubts--not only their own but their friends' and neighbors'. It is no longer sufficient to hold beliefs just because you inherited them. Only if you struggle long and hard with objections to your faith will you be able to provide grounds for your beliefs to skeptics, including yourself, that are plausible rather than ridiculous or offensive. And, just as important for our current situation, such a process will lead you, even after you come to a position of strong faith, to respect and understand those who doubt.
But even as believers should learn to look for reasons behind their faith, skeptics must learn to look for a type of faith hidden within their reasoning. All doubts, however skeptical and cynical they may seem, are really a set of alternate beliefs. You cannot doubt Belief A except from a position of faith in Belief B. For example, if you doubt Christianity because "There can't be just one true religion," you must recognize that this statement is itself an act of faith. No one can prove it empirically, and it is not a universal truth that everyone accepts. If you went to the Middle East and said, "There can't be just one true religion," nearly everyone would say, "Why not?" The reason you doubt Christianity's Belief A is because you hold unprovable Belief B. Every doubt, therefore, is based on a leap of faith.
Some people say, "I don't believe in Christianity because I can't accept the existence of moral absolutes. Everyone should determine moral truth for him- or herself." Is that a statement they can prove to someone who doesn't share it? No, it is a leap of faith, a deep belief that individual rights operate not only in the political sphere but also in the moral. There is no empirical proof for such a position, so the doubt (of moral absolutes) is a leap.
Some will respond to all this, "My doubts are not based on a leap of faith. I have no beliefs about God one way or another. I simply feel no need for God and I am not interested in thinking about it." But hidden beneath this feeling is the very modern American belief that the existence of God is a matter of indifference unless it intersects with my emotional needs. The speaker is betting his or her life that no God exists who would hold you accountable for your beliefs and behavior if you didn't feel the need for him. That may be true or it may not be true, but, again, it is quite a leap of faith.
The only way to doubt Christianity rightly and fairly is to discern the alternate belief under each of your doubts and then to ask yourself what reasons you have for believing it.
* * * * * * *Truth is...there is very little knowing in this life; just looking at clues and making a call.