Synoptic means “taking a common view”. John is the exception to this commonality between Matthew, Mark, and Luke. Some of these variances are that John only records Jesus performing seven miracles, and John covers much of Jesus’ ministry that the other writers do not (much of chapters 2-4 & 7-11) while the others do not. One of the major lessons John teaches about the life changing power of the Christ is not taught be Jesus (ch. 9).
John shines a light on the philosophy of the Christ. It should be noted that Jesus did not teach philosophy in the way the same way a philosophy professor may approach the subject. John records Jesus teaching monotheism (that there is one God), see 10.30, 17.11, 17.21. I believe philosophy is the better term because starting from the perspective of there being only one God, Jesus teaches how mankind should approach their lives. Philosophy can be defined as “a system of principles for guidance in practical affairs.” For John’s perspective of Jesus, this applies.
When people believe in Jesus, according to John, they change their behavior. I heard a preacher advocate for writing “be-leave” at the beginning of the Gospel of John in your Bible. Because when people come to belief in Jesus as the Son of God they leave their current world view and choose a path of righteousness. The word “believe” is used 84 times in John. The other three gospel writes combine to use the word only 32 times. This suggests John is greatly concerned with his readers not just knowing that Jesus was a man, but that He was unique- the Chosen One of God. Why should you believe Jesus is the Christ? -because so many of those who interacted with Him did. “Now Jesus did many other signs in the presence of the disciples, which are not written in this book; but these are written so that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in His name” (20.30-31)
“Now there are also many other things that Jesus did. Were everyone of them to be written, I suppose that the world itself could not contain the books that would be written.” (21.25)