This question becomes the foundation for everything about Christianity, in my mind. For me, while one can presuppose the existence of God and that He/it might want us around and so might try to help us get to Him/it, it would all be based on the imagination or ideas of someone. To accept it would all be on faith alone. That is, by the way, the truth about all religions, that there is no verifiable proof that, say, you can achieve Nirvana or that someone actually was reincarnated or that even Allah exists. If there were no Bible or no way to prove its validity, then Christianity would merely be in the same boat as the others.

Some would want you to think that last statement was true, but they would be wrong. In case you did not know this, I have a MA in history and while that makes me no expert in history, it does give me the right to say I am an historian and that I have experience with things related to this field. As a historian, I can tell you with purpose and clarity that the Bible is the most historically accurate book from antiquity. Of course with the printing press in the 14th century, what makes a work verifiable became a lot easier, but prior to that, we can also verify to some very great detail the veracity of any book from antiquity.

Now, I am going to give you a very, very brief synopsis but you should consider 2 or 3 books for yourself to read and for your friend. First is Lee Stroble's The Case for Christ. Easy to read--a must to put into her hands. Then Josh McDowell's He walked among us and Evidence that demands a Verdict. In those books you will find more information than what I give you.

In general terms, a work from antiquity is judged or examined from a textual point of view and a context point of view. What the book says about its time. If a book was supposed to be written in the Roman period but misplaces an emperor, well that is bad for the verifiable-ness of the book. On the other hand, if a book as absolutely no errors, we often begin to question its authorship, that maybe someone in a later year wrote the work, having the facts before them, making everything perfect.

The issue with works of antiquity is that we don't have the original work, called the autograph. Like when you write a letter or paper (assuming you actually used pen and paper), that is the autograph. There can be only one. Anything else is a copy. Prior to photocopiers, a copy was hand made, so even if you made the copy, there would be a chance for an error to occur. but there would be no errors in the autograph, for it was the first.

Since we don't have autographs for works, in the majority, prior to say the 700s, we are forced to work off of the copies. As I said, that is done through a variety of tests. And the more copies you have, the better off you are so that you can check for errors. Errors can occur naturally enough, just misspellings or switching words around. Sometimes, one could skip a line by accident. Imagine coping word for word the entire book of John. After a while, you would get tired and might make a mistake or two. Those kinds of errors are easily noted and explained.

Again, in general terms, the Bible is about 99.5% accurate. No before you freak out that I did not put 100%, know that the .05% is by and large those simple textual errors that in no way undermines the veracity of the Bible. in fact, I think it strengthens the claim in that you know it was copied by humans, but the margin of error is non-human. Meaning, by all rights, there should be 15-25% error of a textual nature. Its simply incredible how accurate the Bible is.

And the weight of evidence through the copies is overwhelming. If I have my numbers right, there are over 22,000 extant copies of some nature of the Bible from antiquity. To help you get that, the next most copied book was also considered a spiritual book and was read in that light and memorized by the ancients. That was Homer's Illiad. For the Illiad, we have about 600 copies and the most ancient was written around 1000. Meaning, the earliest copy we have is over about 1500 years removed from the original. Aristotle wrote his poetics in 343 BC and the earliest copy we have is 1100 AD, and there are only 5 manuscript copies in existence. Over and over again, in ancient writings, that is the case, small numbers of Manuscripts and a large gap in time between the original and the copy. And no one doubts the content of those works. For the Bible, our earliest copy is about 125 AD, meaning, there is only 100 years between the death of Jesus and this copy speaking about him. and that copy is exactly what you read in your Bible today. Most historians, Christian or not, will tell you that the odds of that being a true fact are astronomical, but it is true for the Bible.

And the Old Testament is just as reliable, if not more so. Again, many copies, very close to the original date of writing.

In every sort of test, the bible blows the field away. Archeological test? Perfect and more is being discovered every day proving what the Bible said is true. Historical? Most non-biased historians will tell you that Dr. Luke is the equal to any of the great ancient historians. On and on I could go—it's overwhelming.

Finally, this is one of the most killing questions to me about the veracity of the Bible. Assume for a moment that what these guys wrote was a lie. Or they embellished a lot. Maybe Jesus lived, but, you know, he really never walked on water or fed people with a few loaves of bread. The disciples just made that up to make him look really spiritual and cool. And that raised from the dead thing, well, let's just not go into that. If that were true, then why would these guys and ladies die for a lie? It makes no sense whatsoever. Sure, some of the later converts could have been persuaded by the lie, like we see in cults today. And sure, one or two of them could have been so intoxicated with that kind of power that they too began to believe the lie (like we see in cults today when the leader also commits suicide for what he believes). But do you really think that hundreds would die knowing it was a lie? I just can't see that. No way. And from history, non-biblical history I might add, we see that several of the key leaders who would be in the know, all died for the truth. Amazing.

Well, hope that helps. Get the Stroble book for readability and the Mcdowell book for the textbook approach.