If the Bible is only a collection of human ideas dreamed up by people many centuries ago, then you might have a point. In other words, if the Bible is just like every other book, we would have reason to decide if we wanted to pay any attention to it.
But the Bible isn't just another human book. The Bible claims to be something far greater than this: It claims to be the Word of God. In other words, it says that behind its human authors was another author: God Himself. The Bible says, "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).
If this is true (and as a Christian I believe it is), then it means we aren't free to pick and choose what parts of the Bible we will believe. The whole Bible is God's Word, and the whole Bible teaches us God's truth. The Bible says, "As for God, his way is perfect; the word of the Lord is flawless" (2 Samuel 22:31).
I realize you may not accept this right now–but I challenge you to begin reading the Bible for yourself. Ask God to show you if it is His Word, and to speak to you through it if it is. Most of all, realize that the whole Bible points to one person, and that person is Jesus Christ. He is the living Word of God–once you discover Him, your life will never be the same.