John is a longer account of Jesus than that in the other Gospels, and gives a sense of the person or people who wrote it
and the beliefs they treasured.
It starts with a recounting of the beginning of Genesis, saying that "In the beginning was the Word, the Word was God, and God is the light of the world--but the darkness doesn't get it."
John the Baptist testified that Jesus was God's light, shining for every human being if they had faith in His name. Jesus was the Word, full of grace and truth.
Jesus went into Jerusalem during Passover and found money changers sitting in the temple. Overturning their tables and driving them out, He said, "Don't make my father's house a place of merchandise."
He taught people they needed to be reborn, of water and the Spirit, to enter into the kingdom of God: Those who don't believe in God are condemned already by the world: the light comes in and they prefer the darkness because their deeds are foul and they want to avoid scrutiny. But they who are carrying out truth move into the light.
Jesus met a woman at the well and as she gave Him a drink, he told her about the Living Water he had to offer. She said she knew she ought to worship in Jerusalem, but Jesus told her people ought to worship not in a place, but in spirit and in truth.
The people wondered if Jesus was trying to seek glory. Jesus said he was trying to seek the glory of the One who sent him. He pointed out that many of them weren't keeping Moses' laws, even though they'd been circumcised as a covenant with God. He was trying to help them ro be whole.
A woman who had committed adultery was about to be stoned. Jesus said, "He that is guiltless among you, be the first one to throw a stone at her." Then the crowd started to leave, the eldest ones first, until only he was left there with her. He told her to go and sin no more.
Jesus healed the sight of a blind man. People thought this sighted man must be a lookalike of the blind man they knew. The man said, "No, it's me, I was healed by Jesus." Then the people believed the man must never have been blind. The man's parents said, "No, he was born blind." The people called Jesus a sinner for working on the Sabbath. The man said, "I don't know about that, but I'm a believer." The people cast the man out from among them. Jesus said, I bring judgement: With faith, the blind might see. Without faith, the seeing are blinded.
Jesus knew all along of the prophesy that one of His disciples was going to betray Him in the end. He broke bread with his disciples for one final Passover. At the moment Judas Iscariot left the dinner table to seemingly go out and get some things, Jesus saw that a cosmic chain of events was about to lead to His death. Glorified by God, Jesus gave a new commandment: "Love one another as I have loved you." He explained, that's how people are going to know you are my disciples; that you love one another.
Jesus taught, "If ye love me, keep my commandments." God's Holy Spirit would teach His followers all things. In contemplating His death, Jesus said, "Peace I leave with you, though not the peace of this world." Before He had to leave, Jesus prayed to God that His people might have a special joy, even as the world persecutes them, and that they might feel God's love until the day they meet with Him in heaven.
The rest of the book gives an account of Jesus' crucifixion and resurrection.
Much of the Book of John affectively sets Jesus' believers apart from 'the world.' In chapter 14, Jesus is said to tell people that they must believe in Him to have eternal life. Even now, the world struggles with such an exclusive statement.
Part of what defines Christianity today is the various churches' level of acceptance of that dictum, in relation to their belief in Jesus' message and teachings. Many people in the world hate Christianity for this claim that only Jesus can bring one to God.
It remains for the reader to decide; is it Jesus' teachor is it only a strong belief in Him that matters?