People write books for many different reasons. John wrote his book so that people would be able to know Christ and have eternal life.
John tries to avoid any praise for himself as he writes. He does not even tell us that he is the author of this book. In the book, he refers to himself as “the disciple who Jesus loved.” He gives us a good example. We should all try to get people to praise Jesus, not ourselves.
John tells us that he wrote so that we would know who Jesus is, and so that we would have life through him. Jesus was the promised one, who’s life was prophesied in the Old Testament. He was God and man. Anyone who trusts in him for forgiveness of sin will certainly be given eternal life.
John wants all of us to take the good news of Jesus Christ to the world. John did his part by writing a book about Jesus. It is our responsibility to explain this book to the peoples of the world.