What is the purpose of the book of John?
Many times it’s a lot harder to figure out the purpose of the book of the Bible because the writers of the New Testament don’t broadcast their purpose in writing. But we don’t have this problem with the Gospel of John.
In John 20:30-31, the apostle gives us the purpose for writing his book. He tells us that these things were written that we may believe that Jesus is the Son of God. This belief will lead us to eternal life in the name of Jesus.
John composes his gospel in what most scholars agree is the two books, the first contains signs and I am statements, and the second book concerns the Passion of Christ, his death and resurrection.
Every one of the signs John gives are meant to give evidence that Jesus is divine. The I am statements look into the Old Testament past, where the name of God (Yahweh) essentially means “I am.” Jesus claims to be God almost every time he says, “I am.”
After he says “I am” he follows it up with an image in the statements. For instance, “I am the Bread of Life.” This image conveys something about Jesus’ entity. In this example the Bread of life refers to his ability to provide for his people.
John gives us an extended Olivet Discourse that expands upon what Jesus said to his disciples in the Upper Room before his arrest and crucifixion (John 13-17). Then John follows along with much of the synoptic Gospels (Matthew, Mark, and Luke) in the Passion narrative about Jesus’ arrest, crucifixion, burial, and resurrection.
John adds 90% unique material from the synoptic Gospels. Much of what he says about Jesus cannot be found in the other three Gospels. He is writing later than the others and presenting a new or different perspective on Jesus.
But his purpose is not to inform or fill in the gaps of the other Gospels. His point of writing later is to look back and record the events of Jesus’ life and ministry that give us the deepest glimpse into him as the Divine Savior of the world. John places a heavy premium on belief in Jesus and his divinity.