That's an excellent question because so much is at stake in the Christian faith in terms of the truthfulness of Scripture. The Bible is our primary source of information about Jesus and about all of those things we embrace as elements of our faith. Of course, if the Bible isn't true, then professing Christians are in serious trouble. I believe the Bible is true. I believe it is the Word of God. As Jesus himself declared of the Scripture, "Your word is truth." But why am I persuaded that the Bible is the truth?
We need to ask a broader question first. How do we know that anything is true? We're asking a technical question in epistemology. How do we test claims of truth? There is a certain kind of
truth that we test through observation, experimentation, eyewitness, examination, and scientific evidence. As far as the history of Jesus is concerned, as far as we know any history, we want to check the stories of Scripture using those means by which historical evidence can be tested — through archaeology, for example. There are certain elements of the Scripture, such as historical claims, that are to be measured by the common standards of historiography. I invite people to do that — to check it out.
Second, we want to test the claims of truth through the test of rationality. Is it logically consistent, or does it speak with a "forked tongue"? We examine the content of Scripture to see if it is coherent. That's another test of truth. One of the most astonishing things, of course, is that the Bible has literally thousands of testable historical prophecies, cases in which events were clearly foretold, and both the foretelling and the fulfillment are a matter of historical
record. The very dimension of the sheer fulfillment of prophecy of the Old Testament Scriptures should be enough to convince anyone that we are dealing with a supernatural piece of literature.
Of course, some theologians have said that with all of the evidence there is that Scripture is true, we can truly embrace it only with the Holy Spirit working in us to overcome our biases and prejudices against Scripture, against God. In theology, this is called the internal testimony of the Holy Spirit. I want to stress at this point that when the Holy Spirit helps me to see the truth of Scripture and to embrace the truth of Scripture, it's not because the Holy Spirit is giving me some special insight that he doesn't give to somebody else or is giving me special
information that nobody else can have. All the Holy Spirit does is change my heart, change my disposition toward the evidence that is already there. I think that God himself has planted within the Scriptures an internal consistency that bears witness that this is his Word.
~ R.C. Sproul, "Tough Questions"