Purpose and Structure
John helpfully tells us his primary purpose in 20:31
But these are written that you may believe that Jesus is the Christ, the Son of God, and that by believing you may have life in His name.
There is some debate over whether the gospel was intended primarily as evangelistic or to build-up existing Christians. There are several examples in the gospel of people coming to believe in Jesus. At the same time there are sections, particularly from chapter 13 onwards, that seem primarily aimed at existing Christians. So I think the answer to the question is both.
The general structure of the gospel is generally agreed to be as follows:
Content and Comparison with the other gospels
John is distinct from the other three gospels. Matthew, Mark and Luke, while having their own distinctive emphases, share a lot of common material and are called the synoptic gospels. John is very different. Most of the action in the synoptics take place in Galilee with six months in the south in Judea. Conversely, most of John is set in Judea. There are no parables nor casting out of demons in John. Key events in the synoptics, such as the transfiguration, the Last Supper, Jesus’ baptism, the temptations and details of His birth are omitted from John. Why is this? Well as we saw earlier John was probably written about 90 AD, so these other gospels were known and there was no point repeating them. John’s gospel is much more reflective and adds a new dimension. Some of the key elements of the gospel are:
the humanity and divinity of Jesus
the intimate teaching of Jesus to His disciples and His prayer for them
the gospel is very trinitarian, with a major emphasis on the relationship between the Father, Son and Holy Spirit
the discourses between Jesus and various people focuses on who Jesus is
there is far more on the Holy Spirit and the believer in John than there is in the synoptics.
John is concerned with our relationship with the Father, Son and Holy Spirit.
Jewish and Greek Characteristics
John was communicating to a Greek world as well as a Hebrew one. It is believed that he was based in Ephesus (in modern day Western Turkey). This has some bearing on the nature of John’s gospel. One of these is the view of time. One aspect of Hebrew thought had a linear view of time, ie past, present and future. So they saw things as travelling towards a conclusion. We see this throughout the Bible with the Day of the Lord being the destination and everything working and leading towards this day. At the same time we should also be aware of the idea of “event time”, ie focusing on an event and the nature of the event, rather than a nice neat chronology. This view is still used in John. However, he also uses the Greek view, which was concerned with life above and below, or heaven and earth. One of the prominent features of John is Jesus being the one who was sent from heaven, and then later on His having to return to heaven so that the Holy Spirit could be sent from heaven to earth.
At the same time there are significant Jewish characteristics to John’s gospel. Israel Abrahams (an excellent Jewish name!), Reader in Rabbinics at Cambridge , said that John’s gospel was the most Jewish of the gospels (Kruse). He said this because of the numerous allusions to the Old Testament, knowledge of the Jewish festivals and their symbolism, and Jesus’ use of rabbinic arguments in his debates with the Jews.
John often refers to “the Jews”. The term is used in a variety of ways in John. The majority of negative references are to the Jewish leadership, and there are no grounds whatsoever for any anti-semitic inferences.