The Gospel of John is known as the "Spiritual Gospel." While the other Gospels focus on what Jesus did, John focuses on who Jesus is and what he meant.
Here is a deep-dive summary of each chapter, concentrating specifically on the core lessons Jesus is trying to teach.
The Logos Unveiled in John.pdf
Jesus is presented as the Logos (The Word). Through his interactions with the first disciples, Jesus teaches that he is the bridge between the finite and the infinite. When he tells Nathanael he will see "angels ascending and descending on the Son of Man," he is teaching that he is the new "Jacob’s Ladder"—the only point of access between Heaven and Earth. He teaches that to see him is to see the light that creates and sustains the universe.
At the wedding in Cana, Jesus teaches that his ministry is one of transformation, not just improvement. By turning water (used for Jewish purification) into wine (the symbol of joy and the New Covenant), he teaches that the old religious systems are being superseded by something far superior. Later, in the Temple, he teaches that the true "House of God" is no longer a building, but his own body. He is teaching that the locus of worship is shifting from a place to a person.
In his midnight conversation with Nicodemus, Jesus teaches the doctrine of regeneration. He explains that human effort and religious heritage are useless for entering the Kingdom; one must be "born from above" by the Spirit. He teaches that the Spirit is like the wind—sovereign and invisible—and that his own coming death (being "lifted up" like the bronze serpent) is the only remedy for the "venom" of sin. He teaches that the motivation for this entire plan is God’s radical love for a rebellious world.
Through the Samaritan woman, Jesus teaches that human desires are symptoms of a deeper spiritual thirst that only he can quench. He teaches that "Living Water" is the Holy Spirit dwelling within the believer. He also teaches a revolutionary view of worship: that God is seeking people who worship in "Spirit and Truth," effectively teaching that race, gender, and geography are irrelevant to God. Finally, he teaches his disciples that his "food" is doing God's will, meaning that spiritual obedience is more sustaining than physical nourishment.
After healing a man on the Sabbath, Jesus gives a lengthy discourse teaching his equality with God. He teaches that he has the "power of life in himself" and the authority to judge the world—two things only God can do. He teaches that he does nothing independently of the Father, but acts in perfect "synchronized" harmony with Him. He teaches that the Jewish Scriptures are not an end in themselves, but a map designed to lead people to Him.