The Bible is certainly a book that has drawn a lot of attention to itself, whether good or bad. It is a controversial book in the eyes of those who do not understand it. But to the children of God, it is not only truth, it is the source of spiritual food and theological authority. There are several reasons why every Christian must read the Bible regularly without fail. The first and foremost reason can be found in John 1:1.
John 1:1 - "In the beginning was the Word, and the Word was with God, and the Word was God."
The Protestant Reformation brought about a Latin phrase, "Sola Scriptura," which means, "by scripture alone." This phrase is referring to the fact that the Scriptures are the sole, inerrant, inspired, authoritative word of God. The Bible is the only source for Christian doctrine. Anything beyond the Scriptures, that does not hinge upon the Scriptures, should be deemed as a heresy or even as apostate. That may sound harsh, but pay close attention to the last four words of the first verse in John's gospel: "the Word was God." Also, Paul said in 1st Corinthians 3:11, "For no man can lay any other foundation than that which is laid, which is Jesus Christ." There is a connection between those two passages, which needs to be explained.
Now, in the context of John 1:1, "the Word" refers to Jesus Christ, and, in the 14th verse, notice that, "the Word was made flesh, and dwelt among us (and we beheld his glory, the glory as of the only begotten of the Father), full of grace and truth." By saying "the only begotten of the Father," the Scriptures are pointing to Jesus Christ, as mentioned in John 3:16, which says, "his only-begotten Son..." Therefore, make this connection: the Word existed with God in the beginning, the Word was manifest in the flesh as God's only-begotten Son, the Word is Jesus Christ, Jesus Christ is God manifest in the flesh, the Word is God; in that, the essence of the Bible is God's Word, which is an extension of God Himself. (If you do not make that connection, you will not understand the significance of the Bible, beyond that of an important book for Christians. That is not to say that the Bible deserves worship. Remember: the Bible is God's Word, but the praise and worship is due to the Speaker of the Word.) This connection gives a strong emphasis to Paul's statement in 1st Corinthians 3:11. That emphasis is this: anything that is not rooted in the Word, namely, Christ, is not of God.
Since Jesus Christ is the Word of God manifest in the flesh, it is imperative for all who are Christians to know both the Word and God. Given that the Word is God, as detailed by John 1:1, in order to know God, a Christian must know His Word. In the same way, in order for a Christian to know the Word, he must know God. One cannot be known without the other. So, this gives a very compelling reason for Christians to read the Bible. If a Christian does not read the Bible, and understand it, he does not know God. Absorbing God's holy Word will bring a Christian to know Him, and in turn God will know, or acknowledge, the Christian. This is similar to what James wrote in James 4:8, saying, "Draw near to God, and he will draw near to you..." (Now, that passage in James was part of a call to repentance for sinners, but the principle holds true for everyone.)
Another compelling reason to read the Bible is for spiritual food, or sustenance. Why is spiritual sustenance necessary? In order for a spirit to remain alive, it must be sustained; therefore, sustenance of some kind is required. God's Word gives life, as detailed in John 1:3-4, which says, "All things were made by him, and without him nothing was made that was made. In him was life, and the life was the light of men." With that in mind, notice the details of the creation outlined in the first chapter of Genesis. Immediately before each stage of creation, the Bible points out that, "And God said..." (You will find this in Genesis 1:3, 6, 9, 11, 14, 20, 24, and 26.) So, God created the universe with His Word. Then finally, after the universe was created, God created man with His Word. But that's not all. Of all His creations, God chose to sustain man with His word. In Matthew 4:4, Jesus said, "It is written, 'Man shall not live by bread alone, but by every word that proceeds out of the mouth of God.'" (Jesus is quoting Deuteronomy 8:3. This is also quoted in Luke 4:4.) However, God, knowing the depravity of mankind, provided the ultimate and eternal form of sustenance: His Son, Jesus Christ, the Word manifest in the flesh. This provision, this sustenance, was offered freely to all mankind, so that those who will believe (God's chosen), may receive the gift of this eternal sustenance (John 3:16). Jesus proclaimed Himself as this eternal sustenance in John 6:47-51, by saying,
Truly, truly, I say to you, he who believes in me has everlasting life. I am that bread of life. Your fathers ate manna in the wilderness, and are dead. This is the bread which comes down from heaven, so that a man may eat of it, and not die. I am the living bread which came down from heaven. If any man eats of this bread, he shall live forever. And the bread that I will give is my flesh, which I will give for the life of the world.
In that, Jesus is declaring Himself, being the Word manifest in the flesh, as the ultimate, and only sustenance which gives life for all eternity with the Father in Heaven. Now, Christ is not literally speaking of eating His flesh. In fact, the Jews to whom He was speaking did not understand this (John 6:52), because He spoke this in a parable. Even His disciples thought of it as confusing, to which they asked Jesus in John 6:60, "This is a hard saying. Who can hear it?" Jesus' response was very clear and concise, which contains the key to the parable He spoke. In John 6:63, Jesus said, "The words that I speak to you, they are spirit, and they are life." It is the Holy Spirit, whom Christ sent from the Father (John 15:26), who helps, or enables God's chosen ones to discern and, in a sense, digest, God's Word (bread of life, living bread, flesh of Christ—Jesus Christ) for the nutrients which truly satisfy the soul.
The importance of the Bible for a Christian is not only a book which must be read, but it is also the means by which a Christian knows God, and receives the sustaining bread for the soul. No doctrine or prophecy can be measured against anything but the Word of God in the Bible. If a doctrine or prophecy is not rooted in the Word, it is not from God. If a Christian regularly reads the Bible without fail, he will have the ability to discern such things by knowing God and His will. Through seeking God's desires, a Christian will obtain the necessary sustenance for his soul and thrive on the bread of life given by Jesus Christ as God's holy Word manifest in the flesh. His words are spirit. His words are life.