John the Apostle recorded his eyewitness account in his gospel. It is different from the other gospels. The three previous gospels recorded by Matthew, Mark, and Luke are called the synoptic gospels for a reason. These other writers followed a similar format that recounts the life, teaching, and work of Jesus Christ's earthly ministry. As such, the placement of John's gospel in Scripture builds upon the historical narratives written by the others. John's gospel focuses on the importance of having faith in Jesus Christ-the Messiah and the Son of God.
There is material in the other gospels that John chose not to include. It is not that this material was unimportant, but it was already covered in the others. This includes His testing in the wilderness, Jesus' transfiguration, the discourse during the Lord's Supper, the Sermon on the Mount, or the exorcism of demons. The Lord's Prayer and many of Jesus' parables are not found in this gospel.
John is intent on presenting the deity of Jesus Who existed prior to Creation. "In the beginning was the Word, and the Word was with God, and the Word was God. The same was in the beginning with God. All things were made by him; and without him was not any thing made that was made" (Jn. 1:1-3).
The Gospel of John shows that Jesus is the Messiah of Israel and the Son of God. The God Who sent Moses to deliver Israel from Egypt is the same God Who sent His Son to save Israel from their sin.