To be considered valid, any theory must be falsifiable. That is, there must be something, which if found, can prove the theory false. For example, the theory of evolution would be proven wrong if a skeleton of homo sapiens were found in rock that was a million years old. Similarly, any religion can be proven wrong if any of its structural doctrine can be proven wrong.
Since Christians believe that the Bible is the literal word of God, everything expressed in the Bible must therefore be true. All that is necessary then to falsify the bible is to find one thing in it that is not true. If there is one thing that can be found in the bible that is irrefutably not true, then the Bible, and hence the Christian religion is false. Amazingly, Jesus own words provide examples of things in the bible that are not true.