That question is a most sensible one to ask. Obviously, if it is simply a collection of good stories, it does not deserve the weight, authority, or trust it does if is actually the Living Word of God. While there are many ways we can be certain that the book we call the Bible is actually the Word of God without error or mistake, I will immediately cite six points for reference.
First, the Bible claims this itself: “All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, that the man of God may be complete, thoroughly equipped for every good work” (2 Tim. 3:16–17). Inspiration has the idea of “God-breathed.” Although God used human men to write the Scriptures, He was in fact writing through them. If God wrote the Scriptures, then from that we also know that the Scriptures are without error. A holy God could not breathe a lie: “knowing this first, that no prophecy of Scripture is of any private interpretation, for prophecy never came by the will of man, but holy men of God spoke as they were moved by the Holy Spirit” (2 Pet. 1:20–21). If human law claims that all are innocent until proven guilty, then the Bible is what it says it is until proven otherwise.
Secondly, Jesus Christ Himself recognized the Scriptures as the authentic Word of God. On numerous occasions, Christ recognized the Old Testament as written by God. When tempted by Satan, Christ said, "It is written” (Matt. 4:1–11) three times alluding to the Old Testament. He also referred to the Old Testament as the Word of God (Mark 7:9–13). Even the familiar story of Jonah and the big fish was regarded by Christ as a story true in its details and recorded by God for a divine purpose (Matt. 12:39–41).
Thirdly, the Bible has impeccable continuity. Over a period expanding 1600 years, God used more than 40 authors to write the Scriptures. These men were from all kinds of backgrounds, including fishermen, kings, physicians, poets and philosophers. Although they wrote on a wide range of subjects from the creation of the world to the end time events, there is such continuity in their thoughts and facts that the Bible is seen as one book instead of a collection of 66 different books.
Fourthly, the Bible speaks of truth divinely revealed. It speaks of details of creation, heaven, hell, and the sequence of end time events. These are all beyond human discovery and knowledge. Also, none of these details contradict one another and all have a particular place and sequence in a divine scheme. The fact that it calls out items that were completely unknowable at the time of origin proves that the Bible is a book of divine authorship.
Fifthly, the Bible’s transforming power is unequalled. The Bible is considered the greatest piece of Literature ever written and has grasped the attention of those of all ages, backgrounds, and education. Its depth of wisdom is incomparable to any other book. Beyond that, though, no book has transformed lives the way the Bible has. Multitudes have found a personal relationship with God through Jesus Christ from reading its pages and the lives of multitudes have been transformed through reading its truths. It does what it promises to do: “For the word of God is living and powerful, and sharper than any two-edged sword, piercing even to the division of soul and spirit, and of joints and marrow, and is a discerner of the thoughts and intents of the heart” (Heb. 4:12).
Lastly, the Bible has stood the test of time. There is no other book that has been published in more languages and in more cultures than the Bible. The Frenchman, Voltaire mocked the Bible in the past, yet many in our present century, too, have predicted that the Bible would become an obsolete book. Even still, the Bible continues to be the most demanded book worldwide, which is a testimony to its author, God Himself.
Anyone who looks at the Bible objectively and examines the above facts surrounding it has to come to the conclusion many others have: this is indeed the Word of God. That understood, nothing is more important than to know what it says.