If the Bible were like every other book that's ever been written, then I'd probably agree with you. Why base our lives on an ancient book that might or might not be true?
But the Bible claims to be far different: It claims to be from God Himself. God used humans to write it down -- but behind the scenes He was at work by His Holy Spirit, directing and helping them write what He wanted them to say. And because it came from God, its message is timeless -- because God is timeless. The Bible puts it this way: "For prophecy never had its origin in the will of man, but men spoke from God as they were carried along by the Holy Spirit" (2 Peter 1:21).
Why do I believe the Bible is God's Word? First, because its message is consistent from one end to the other -- the message that God made us and loves us, and wants us to know Him and live with Him forever. Second, because when we read the Bible with an open heart and mind, we hear His voice telling us that its message is true.
But most of all, I believe the Bible because it points us to Jesus Christ, who is the living Word of God. He is the ultimate proof that God loves us, because He came from heaven to give His life for us. Discover the Bible for yourself -- but most of all, make Christ the foundation and center of your life by asking Him to come into your life today.