Because it is the inspired Word of God. It is his instruction manual to us. It his love letter to us. Every word is true and it provides us with the weapons we need to fight off the enemy when he speaks lies to us. The Word is the sword of the Spirit and is used to combat the lies of the one that would try to tell you that you are anything less than a child of the living God.
You need to read it daily and meditate on it day and night. God will speak to your heart as you read the Bible. The more intimately you know the scriptures, you will find yourself remembering verses that speak to different situations that you face. All the answers that you need are found there. That is why you should read the Bible!
2 Timothy 3:16 (NLT) - “All Scripture is inspired by God and is useful to teach us what is true and to make us realize what is wrong in our lives. It corrects us when we are wrong and teaches us to do what is right.”