What distinguishes Christians from other theists is that we don't just believe in a god, but we believe in the God who has revealed himself through the Scriptures - the Bible. But why do we have such a high confidence in this ancient manuscript? And why do we accept some of the accounts that some find so hard to believe? The creation of the world in six days. All the animals in Noah's Ark during a worldwide flood. Jonah in the belly of a fish for three days, and so on.
First, how do we know that these stories have not been embellished over the years? After all some of these accounts are several thousand years old. Well, this is easy to answer, because the Bible is the most accurately preserved ancient document bar none. The sheer volume of documents from all over the ancient world, means that if any one copyist introduced an error, it would be easy to spot by cross-referencing against the thousands of other manuscripts in existence. Indeed some minor inconsistencies were inevitably found this way. Any good translation of the Bible that you can buy today will not hide these but provide a footnote saying what the alternative manuscripts say. However the differences in meaning these alternative renderings give are almost always subtle, usually inconsequential, and never do they introduce a whole new concept out of thin-air!
So we know that the Bible we have today is an accurate version of the original documents as they were first recorded. We cannot therefore just dismiss what the Bible says, we must either accept it or reject it.
I want to focus on just one of these miraculous accounts. The account of the resurrection. For if the resurrection of Christ is untrue, then Christianity is false, the Bible is irrelevant, and there is no point continuing any further. But if the resurrection is fact, then it means that God can do anything - nothing is impossible for him. If Jesus was truly raised then this surely means that he was who he claimed to be - God incarnate, and everything he said, including his validation of all these Old Testament accounts is also true.
It all stands or falls on the resurrection. If Christ is raised from the dead, then no matter what other intellectual questions you still have, Christianity must be true. If he was not raised, no matter how accurately preserved the Bible is, it must be false.
If Christ has not been raised, your faith is futile and you are still in your sins. (1Corinthians 15:17)
Now we have already asserted that our New Testament is an accurate version of what was originally written. But we also know that the New Testament was finished around 70AD only 40 years after the death of Christ, and some of the manuscripts date from as early as 50AD only 20 years after his death. We also know that Jesus preached to thousands. If what was written about Jesus' life was fictitious there would have still been multitudes of people who could have come forward and denounced it.
F. F. Bruce, Rylands professor of biblical criticism and exegesis at the University of Manchester, says concerning the value of the New Testament records as primary sources: "Had there been any tendency to depart from the facts in any material respect, the possible presence of hostile witnesses in the audience would have served as a further corrective."
But the same is also true for his resurrection:
For I delivered to you as of first importance what I also received: that Christ died for our sins in accordance with the Scriptures, that he was buried, that he was raised on the third day in accordance with the Scriptures, and that he appeared to Cephas, then to the twelve. Then he appeared to more than five hundred brothers at one time, most of whom are still alive, though some have fallen asleep. (1Corinthians 15:3-6)
That which was from the beginning, which we have heard, which we have seen with our eyes, which we looked upon and have touched with our hands, concerning the word of life. (1John 1:1)
As well as the authors, there were over five hundred eye-witnesses at the time the manuscripts were written who could testify that Jesus was raised from the dead. Substantial evidence by any standards.
But the evidence does not end there for Jesus said that after he was raised from the dead, he would pour out the Holy Spirit upon his believers, and that they would continue to do the works that he had done. Healing the sick, delivering the oppressed, and other signs that would follow. The ongoing miraculous power of the Holy Spirit in the lives of believers is further proof that Jesus was indeed raised.
Athanasius writing in the fourth century after Christ said this:
In a word, then, those who disbelieve in the resurrection have no support in facts, if their gods and evil spirits do not drive away the supposedly dead Christ. Rather, it is He Who convicts them of being dead.
We are agreed that a dead person can do nothing: yet the Savior works mightily every day, drawing men to religion, persuading them to virtue, teaching them about immortality, quickening their thirst for heavenly things, revealing the knowledge of the Father, inspiring strength in face of death, manifesting Himself to each, and displacing the irreligion of idols; while the gods and evil spirits of the unbelievers can do none of these things, but rather become dead at Christ's presence, all their ostentation barren and void.
By the sign of the cross, on the contrary, all magic is stayed, all sorcery confounded, all the idols are abandoned and deserted, and all senseless pleasure ceases, as the eye of faith looks up from earth to heaven. Whom, then, are we to call dead? Shall we call Christ dead, Who effects all this? But the dead have not the faculty to effect anything. Or shall we call death dead, which effects nothing whatever, but lies as lifeless and ineffective as are the evil spirits and the idols?
The Son of God, "living and effective," is active every day and effects the salvation of all; but death is daily proved to be stripped of all its strength, and it is the idols and the evil spirits who are dead, not He. No room for doubt remains, therefore, concerning the resurrection of His body.
So the short answer to the original question is faith. Faith that Jesus was raised from the dead, without which none can claim to be a Christian. Faith that this proves who he said he was, the Son of God. Faith that is means that every word from his mouth is trustworthy and true, and so his validation of the Scriptures are all we need. Faith that the God who raised Jesus from the dead, can do anything.
I'm impressed with the scientist who can solve three-dimensional differential equations in his head, but I'm more impressed in the God who raised Jesus from the dead. I'm impressed with the astronomer whose telescope can look back to the dawn of time, but I'm more impressed with the God who was there when it happened. I'm impressed with all the clever people from whatever their field, zoology, palaeontology, geology; but I'm more impressed by the one who spoke everything that they study into existence. Why do I believe it? Because the Jesus who rose from the dead said that not the smallest letter from all the Scriptures would ever be shown false or void. That's good enough for me!