These are written down so you will believe that Jesus is the Messiah, the Son of God, and in the act of believing, have real and eternal life in the way he personally revealed it. (John 20:31 MSG)
But these are written, that ye might believe that Jesus is the Christ, the Son of God; and that believing ye might have life through his name. (John 20:31 KJV)
John had lived with Jesus, eaten with Jesus, and walked many dusty roads with Jesus. John had heard Jesus teach. He had seen Jesus perform miracles. Surely there were many long conversations as Jesus walked from town to town with the disciples. John knew that Jesus was the promised one - The Messiah. And he needed to share that information with others.
So he wrote the Gospel of John for us to read today. John shared the good news so that we would know and believe.
We read the Bible today to learn about Christ. As we learn, our faith is deepened and our belief is strengthened. Through belief, we are given the gift of forgiveness and ultimately the gift of eternal life with Jesus.