This question was asked at an apologetics conference I had spoken at. It is a common question given the fact that many skeptics will not accept any statement of scripture as being part of an argument for the Christian position. They will say something along the lines of: “You can’t use the Bible to prove the Bible”. At this point, the Christian will often scramble to marshal various facts from secular history and science in order to formulate a response to the skeptic. I can sympathize with the believer who struggles with this. It can be difficult at times to think outside our comfort zone into areas that we may not be that familiar with. However, I do not think the believer should be overly concerned at this point.
Notice the question being asked: How do you defend the faith when you can’t use scripture? This is an interesting request of the unbeliever: Defend your faith without using the very thing that defines what your faith is. I was asked once by an atheist to prove the Bible without using the Bible. I responded that I would be happy to if he was willing to prove atheism by only using the Bible. The atheist was not at all thrilled with trying to make his point in accordance with my warped standard proof. Likewise, I pointed out that there is no reason for me to accept his unwarranted standard of proof. Think about it. One does not prove the reliability of the eyes, while closing their eyes shut, do they? In like fashion, when I am presenting the case for the biblical position, I see the Bible as a very vital aspect of that demonstration.
On the other, there is nothing wrong with appealing to evidence for the Christian position outside the Bible. Indeed, since all truth is God’s truth, one can utilize helpful evidences for the Bible in sources outside the Bible. However, I do not appeal to sources outside the Bible within an intellectual framework that is alien to the Bible. It is the worldview presented in the Bible that provides for me a coherent framework in which evidences external to the Bible make sense and have meaning. For the believer, the Bible is more than just a book; it is an interpretive lens and outlook on the world. The skeptic also has a lens or worldview in which he tries to make sense of the world around him. I am not sure if the skeptic would like it very much if we demanded that he prove his position while not utilizing the framework that gives meaning to his system of thought.
As Christians, we do not lay aside our intellectual lens to meet the unwarranted standard of the unbeliever. Likewise, we invite the unbeliever to come to the argument so to speak using his own intellectual lens. It is the task of the apologist to point out that the lens that the unbeliever is using is inadequate. Now merely saying this does not prove it, but I think for the purposes of answering the question presented at the beginning, I think enough has been said that while the believer has a whole host of extra-biblical material to appeal to, he need not lay aside his Bible given that the Bible is the foundation and source of the Christian’s beliefs. If the Christian is to defend the “Christian” faith, and the Bible is the source of the Christian faith, then it would seem to follow that the Bible should not be set aside, but rather, stand front and center in the discussion.