by Matt Slick
We should believe the Bible because it is the word of God. In other words, we should always believe what God says because, well, that's what God says. Yeah, I know that answer may not be sufficient for a lot of people, but the logic is sound. The Bible claims to be the word of God. If it is, then we should believe it. If it is not, we shouldn't. So, is it or isn't it?
Some people will demand complicated proofs to show that the Bible is the word of God. Others will accept archaeological evidences, or independent writings, or something else. Then again, there will be people who will recognize its truth as coming from God. Many people just know there's something special about Jesus, his work, and when they read the Bible they experience its power and truth. And, of course, there will be others who won't accept the Bible no matter what.
But asking why we should believe in the Bible is different than asking why different people believe in the Bible. Asking "Why should we believe God?" is a different question than "What are the reasons different people believe in God?" God exists. Therefore, we ought to believe in him because that is what is right. But different people believe in God for different reasons.
Anyway, we ought to believe the Bible because the Bible is the word of God, but convincing people that it is the word of God isn't easy. We could look to fulfilled prophecies, the power of it's truths, the records of the resurrection of Christ in the Gospels, and evidence for its inspiration. If we believe what's contained in the Bible, then we should believe in the Bible.
The Roman Catholic Church would tell you that you must believe the Bible because they claim to be the true church and they claim that they gave us the Bible. They aren't and they didn't. The Mormons will tell us to believe the Bible in so far as it is currently translated (LDS article of faith eight). The Jehovah's Witnesses will tell you to believe the Bible because it is the word of God and they are the ones who will tell you what it really means.
Ultimately, we should believe the Bible because it is authoritative, true, and is from God. In fact, the Bible never defends itself. It just claims to be the word of God.