Biblical Studies/New Testament Commentaries/The Gospel of John/Introduction

Authorship and Date Written.
Wikipedia Article
"John: The last Gospel" - Introduction:
"John" is the fourth and last Gospel in the New Testament. This Gospel contains many distinctive accounts that are not found in the other Gospels. Only about 10% of the Johannine Gospel is shared with the Synoptic Gospels of Matthew, Mark and Luke. The differences of note include:
Some may argue that this gospel contains many of the principles that would become instrumental in later missionary developments. The fact that most of the book is centered around Jesus' work on earth would also lead many to this distinction about the book.
The similar relationships between the Fourth Gospel and the Synoptics are the accounts of the passion story, basic structural similarity with order of Jesus' ministry, and similar pattern of dialogues/metaphors (Dodd, 1953). On the other hand in the Fourth Gospel there is no account of several common themes from the Synoptic Gospels:
In comparison, the Synoptics have no wedding at Cana, no raising of Lazarus, no washing of the feet of the disciples, and no conversation with Nicodemus.
The literary structure of the story of Jesus flows by a public ministry of Jesus, a private teaching of his disciples, a public trial and execution, and a series of private appearances to his disciples. The author leads the reader through sequences and the reader experiences the story through their emotions. The use of emotion helps the book create a different kind of connection in the reader. Instead of merely presenting the story of Jesus' life in a vague unevoking manner, the author uses words and phrasing to create emotional attachment. It is almost as if the book was written with the intention that it would be used to evangelize those who read it, which of course is the purpose of all the Gospels-- To bear witness to the Truth of Scripture and God's purposes toward men.
Although one would perhaps ask why there are such differences, it is clear that John's Gospel is directed toward those who already are familiar with one or more of the Synoptic Gospels. Thus, John does not repeat the Synoptic content but concentrates on the compelling Personage and Purpose of Christ. 
Finally, some individuals might say the purpose of its writings are to evoke faith or convince readers that Jesus is the Messiah. John 20:31 states, "But these are written, that you may believe that Jesus is the Christ, the Son of God: and that believing, you may have life in his name." It appears, from this verse, that the purpose of the Fourth Gospel is to evangelize its readers. However, scholars debate about the translation of the original Greek. Some say the translation reads, "may continue to believe." If this is the case, the Gospel of John was probably written to strengthen Christians in their struggles at the time (see John 20:28). Robert Kysar, author of "John the Maverick Gospel" believes that the latter purpose mentioned, that the Fourth Gospel was written to sustain Christians' faith, makes sense when the Fourth Gospel, as a whole, is studied. Kysar points out that the Gospel of John consistently shows Jesus as both "sent from God and one who has divine status but is still subordinate to the Father" (Kysar 21). Perhaps this was a response to all the Jewish people who were hesitant about Christianity, charging it with being a religion that supports two gods. When the historical struggle between Jews, who were afraid of losing the "stability of the synagogue" (Kysar 21), and Christians, who were afraid of not being able to practice what they believed, is taken into account, it makes a great deal more sense to view the Gospel of John as an attempt to strengthen Christians' beliefs so they could defend themselves when their faith was questioned.
The themes in this Gospel are all related to the claims which Jesus made about himself, and the evidence that supports those claims. Here are eight claims which Jesus made about himself:
1) That he can give (and is) living water.
2) That he is the bread of life
3) That he is the light of the world
4) That he is the door of the sheep
5) That he is the good shepherd who gives his life for the sheep
6) That he is the resurrection and the life
7) That he is the way, the truth, and the life
8) That he is the true vine
9) That he and the Father are one.
Notice that "living" or "life" appears repeatedly in these claims. Life is a very prominent theme in John's Gospel, and light is closely related to it. Evidence is presented to convince the reader of the truth of the above and other similar claims. Therefore, faith and believing are also prominent themes.
General Resources on the Gospel of John.
The Johannine Literature Web