Critics of evangelical Christianity (and at least two regulars here at Suite101 Protestantism) routinely charge that Bible-believing Christians shouldn't "use the Bible to prove the Bible." Let's examine this:
1. What is the Bible?
Evangelical, Bible-believing Christians will answer that the Bible is the "Word of God." This is an answer based on faith - faith that God indeed supernaturally inspired the writers of the Bible to communicate His divine revelation to its readers.
Christians who hold to this view will cite biblical references to bolster it. These citations ARE legitimate in the sense that they prove that divine inspiration is claimed by the authors of Scripture. It would make little sense for someone today to claim that the Bible is the inspired Word of God....IF....the Bible never made such a claim for itself. So, it IS valid to cite biblical references to prove that the Bible does proclaim itself to be the Word of God.
Side Note: I recognize that the doctrine of biblical inspiration is more complex than stated above. Here it is in a nutshell - at least for evangelicals: 1) Divine inspiration is claimed for "Scripture" and for "prophecy." This is easily seen in the manuscripts. 2) Evangelical Christians believe that these Scriptures and prophecies, which are divinely inspired, comprise the Bible. The canonization process confirmed this. 3) Since the contents of the Bible - i.e., the 66 books - all of which recognized as divinely inspired Scripture - represent the written revelation of God, then - ergo - the Bible is God's Word.
HOWEVER...setting aside the debate over divine biblical inspiration, the Bible MUST then be considered NOT as a unit, but as a collection of first-century ancient writings* endorsed by the overwhelming majority of Christian congregations. This was the case from their authorship until these texts were confirmed in the official Christian "canon" in the late 4th century AD.
*Some liberal scholars hold that a few of the New Testament books were written at the beginning of the second century, but this is no longer the majority New Testament scholarship view.
2. You CAN use one witness to validate another
If you have one witness to an event, you absolutely, positively CAN and SHOULD use another witness (or another two or three witnesses) to help bolster the first witness' story. This is possible with many of the New Testament authors.
Again, the New Testament was originally NOT the "New Testament," nor was it part of the "Bible." Those terms came about during the canonization process which lasted from the 2nd century through the 4th century AD. Originally, these were narratives and letters written by followers of Jesus Christ OR followers of the followers of Jesus Christ.
What we have are FOUR first-century narratives that give us important details of the life of Jesus. While there are differences on minor points (the exact wording of the sign on Jesus' cross, the order of Jesus' post-Resurrection appearances, etc.), the major points between the Gospels are corroborated. The Gospels (certainly the first three - the Synoptics) agree FAR MORE than they disagree.
What does all this mean? Simple: You have FOUR crucifixion accounts of Jesus Christ - NOT one. Any person who says there is only ONE crucifixion account - i.e., the Bible's - is guilty of very superficial thinking and has very little understanding of how history is studied. There is not one account of Jesus' life. There are FOUR ancient accounts of Jesus' life, which have been compiled (for our benefit) under one cover.
Not only are there four accounts of Jesus' life, but some of the information in the Gospels are further corroborated by epistles written between Christian leaders and congregations in the first century.
A critic of Christianity should not be allowed to wave this all aside with a simple "You can't use the Bible to prove the Bible" statement. With due respect to my readers, that is a very thin retort.
3. The Bible Deserves Respect
The books of the Bible warrant the same historical respect that any other ancient document deserves. There is an unfounded, and frankly very unfair, bias against the Bible - which an intelligent and enlightened society should not be allowed to get away with.
It's almost as if the Bible is presumed false until proven true - or, put another way, is not regarded as a valid source of information unless backed up by OTHER documents (normally two or more). In other words, if an ancient document records a historical figure doing something, there is normally a presumption of at least general or relative accuracy applied. The exception is if other information or other sources cast too much doubt on the episode for it to be sustained. The Bible doesn't naturally enjoy this credibility from some scholars, especially (and not surprisingly) liberal scholars. If the Bible records something, it's assumed to be wrong or dismissed until validated by a non-biblical source. This prejudice is unfair.
We have four very clear, ancient accounts of Jesus' public ministry. These should be treated with respect, especially in light of the corroborating archaelogical discoveries and non-biblical sources. (The crucifixion of Jesus, for example, is recorded not just in the biblical record, but in other ancient writings as well).
It's time for critics of evangelical Christianity to set aside their bias and prejudice against the biblical record and to open-mindedly confront the claims of Christianity.