Introduction
Having discussed the business of Christianity in a nutshell, we will consider the matter of the Bible. Because it is always at the root of all things Christian, what the Bible is, why it matters, and how we must use it are all critical questions for the Christian to answer.
The Bible is the very foundation of Christianity. There is nothing that we know of God or can know of God that is not in the bible. Although we could certainly learn plenty from considering the physical universe, even what we learn there requires the corroboration, clarification, and expansion of the Bible.
Like the Athenians who knew that God does exist and was apart from all the other gods and superstitions that they worshipped or adhered to—so much so that they built an altar to Him and acknowledged Him as the unknown God—anyone can learn the fact of God’s existence and gain an idea of His character from creation around him or her. 
However, the knowledge of this God and the understanding of His purpose for the universe that He made and therefore for us individually too are simply not available merely from observing or studying creation itself. Creation was only designed to tell us of His existence and His character, not to actually disclose Who He is to us or tell us much about His plan for it. These latter things are the exclusive preserve of the Bible.
To the Chief Musician. A Psalm of David.
​1 The heavens declare the glory of God;
And the firmament shows His handiwork.
2 Day unto day utters speech,
And night unto night reveals knowledge.
3 There is no speech nor language
Where their voice is not heard.
4 Their line has gone out through all the earth,
And their words to the end of the world.
In them He has set a tabernacle for the sun,
5 Which is like a bridegroom coming out of his chamber,
And rejoices like a strong man to run its race.
6 Its rising is from one end of heaven,
And its circuit to the other end;
And there is nothing hidden from its heat.
7 The law of the LORD is perfect, converting the soul;
The testimony of the LORD is sure, making wise the simple;
8 The statutes of the LORD are right, rejoicing the heart;
The commandment of the LORD is pure, enlightening the eyes;
9 The fear of the LORD is clean, enduring forever;
The judgments of the LORD are true and righteous altogether.
10 More to be desired are they than gold,
Yea, than much fine gold;
Sweeter also than honey and the honeycomb.
11 Moreover by them Your servant is warned,
And in keeping them there is great reward.
Psalms 19:1-11 (NKJV)
18 For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who suppress the truth in unrighteousness, 19 because what may be known of God is manifest in them, for God has shown it to them. 20 For since the creation of the world His invisible attributes are clearly seen, being understood by the things that are made, even His eternal power and Godhead, so that they are without excuse
Romans 1:18-20 (NKJV)
As the excerpt from Psalm 19 above shows, whereas physical creation tells us of God’s existence and of His basic goodness and justice, it is the Word of God that actually makes us wise, that is, that makes us understanding of God Who is Wisdom itself.
The Bible is a book that God Himself put together to tell us of Himself and His Plan. In it, we learn not just His power and deity but also His Person and His “thinking.”
Why is this important?
5 For even if there are so-called gods, whether in heaven or on earth (as there are many gods and many lords), 6 yet for us there is one God, the Father, of whom are all things, and we for Him; and one Lord Jesus Christ, through whom are all things, and through whom we live.
1 Corinthians 8:5-6 (NKJV)
There are many creatures claiming to be God or claimed to be God. In fact, creature history has a great deal to do with Satan’s own aspiration to Godhead. Because he wanted God’s throne, he started a rebellion among the angels that eventually led to the destruction of the first universe. This was only the first instance of creaturely ambition to be God. Today, a multiplicity of human beings and rebel angels aspire to be worshipped as God too (see Daniel 6:6-9 and Acts 12:22-23, for example). How can we tell who the true God is in the midst of this cacophony of claims if we didn’t have the Bible?
This is why the Bible calls itself the Book of Truth:
21 but first I will tell you what is written in the Book of Truth. (No one supports me against them except Michael, your prince.
Daniel 10:21 (NIV)
The fundamental truth of creation is who the true God is. This is because the meaning of creation, the point of our lives is determined by whoever the true God is. All creation answers to whoever the true God is. That is, we individually answer to this God for the choices we make while alive in this world. Our beliefs about God then direct our philosophies and actions.
Seeing how important this question is then, it only follows that a God of Love, such as the God revealed in the Bible is, would provide a witness for Himself, a way to find Him and get to know Him and walk with Him in this world of chaos. Thus, the Bible.
It is reasonable to ask why God does not just make the full knowledge of Himself and His Will accessible through creation. After all, He loves us and wants us to know Him. Why then does He “hide” Himself (Isaiah 45:15; cf. Isaiah 57:17; Psalm 44:24; 13:1; 89:46; Job 13:24; Deuteronomy 32:20)? 
The answer to this is free will. We get to choose whether we want to know God or not. We are not assaulted with knowledge of Him that we don’t want. It is up to us to decide whether we want to get to know God and learn of His Will so that we can adjust our lives to fit it.
6 From one man he made all the nations, that they should inhabit the whole earth; and he marked out their appointed times in history and the boundaries of their lands. 27 God did this so that they would seek him and perhaps reach out for him and find him, though he is not far from any one of us.
Acts 17:26-27 (NIV)
As the passage above makes clear, it is precisely God wants us to “seek” Him and “reach out for” Him that He made things the way they are. He doesn’t want us to not have to actually put in the work. The necessity to put in the work makes it our own thing.
We can also see from the passage that He is really not far from any of us at all. In fact, the bible tells us that the earth is full of His glory (Isaiah 6:3). All of creation is suffused with an unmistakable testimony of Him, even if it doesn’t go anywhere near as far as the Bible goes in telling us who He is and what His Plan is. We all have enough in creation around and within us to lead us to the Bible where we can learn all that He has to teach us about Himself, but creation was designed to also allow us to refuse to heed its call to seek Him.
For those of us who heed creation’s call to seek God, the Bible is the natural next step. As we have said before, it is true that there are other books, traditions, and “revelations” that equally claim to tell us about God. We can always tell just how true any of their claims is by weighing what they say against what is clearly manifest in creation around and within us. That test will prove every time that the bible is the authority to trust regarding who God is and what His Plan for creation is and that all other books etc are lies.