If Christianity is true, then it should be verifiable outside of itself. the bible should be unnecesary in order to prove the truth of Christianity. If any religion is TRUE, then it has to possess a quality of universal believability. Religion has to be universal, or it cannot be true, because truth is universal. I speak of Truth in the grandiose scheme, not in the everyday scheme. Truth has to be universal, or else it would not be truth, only opinion. If religion is the truth, then it has to universally true, but no religion is universal. Since religion is designed for and by humans alone (all other animals and plants having no need for it) it is up to us to detemine the criteria for religion's truth. Since no one religion can claim universal belief across the board, it stands to reason we have not yet found a religion that is the truth, except for morality. Morality, is universally agreed upon, by those capable of understanding morality. No one believes murder to be the right thing to do (psychopaths are unable to understand that murder is wrong, because of brain abnormalities). Lying is universally agreed to be wrong, even by those who do it constantly to gain the upper hand. Morality is the one area that all of humanity agrees on, and it is the church of humanism that preaches morality as it's "dogma" if you will. If there is a qualifying religion in regards to truth, it would have to be secularism, humanism, non-supernaturalism, whatever you'd like to call it.
There are those who would say their religion is not universal yet, but will soon be, we just haven't waited long enough. Certainly the abrahamic religions all count on this. I would say this: If one particular religion is true and others are false, then it is a colossal waste of time (if you are the deity) to allow the other religions to persist. Why not be universal in your coverage. The very fact that there are so many other religions points all too clearly to each of them being manmade, otherwise there would never have been any religions but one. A monotheistic god would be unsatisfied with partial acceptance of his decrees, commandments, and indeed his very existence. The idea that a monotheistic god wants only those adherents who come to him voluntarily is silly, in that any religion (TRUE) that can only attract a certain portion of the population cannot in good consciousness claim itself to be the one True religion. Since it is the Truth, shouldn't it be unabashedly clear to anyone who ever comes into contact with it, that it is the way to follow? There should never be any question in the minds of us, if there is one true religion. There should be no such things as atheists. We should not be able to turn away from the trueist religion. But of course we can and do. Our very presence is testament to the inadequacies of religion. The very presence of so many contradictory religions is testament to the inadequacies of them all. The only universal thought process we have is secularism. Nature is going nowhere, and there is no other nature to compete with the one we have. There is no avenue of deniability about nature's truth or existence. It is here for all to see and enjoy. If we can't universally agree upon something, it cannot be the truth. Science searches for the grand unifying theory of the four forces of nature, Gravity, electro-magnetism, The Strong Nuclear Force and the Weak Nuclear force. Science does not have a grand unifying theory yet and so it (science in general) does not purport to have found that Einstein's special theory or general theory of relativity is the theory that explains it all. Neither does science say that Quantum theory explains everything. Neither do the two theories agree with each other. Universality of agreement and acceptance is required if something is to claim itself as the Truth. No religion can claim itself to be the Truth, precisely because no religion is universal in its acceptance or agreement. We do not need more watering down of the religions that exist, we need a completely new religion. A religion that is accepted everywhere by everyone. We already have this religion, it is called Life. So go live it.