Caution is essential when we're trying to determine the theme of a particular book of scripture. For instance, as we read John's Gospel, it's easy to see themes that deal with the glory which the Father has given to the Son (John 1:14) as well as the theme of divine agency (John 1:1-3). Furthermore, it appears that John clearly presents the two motifs of KATABASIS and ANABASIS that are intimately connected with the event mentioned in 1:14. And think of how the Apostle concludes chapter 20 of his Gospel: "But these have been written down that you may believe that Jesus is the Christ the Son of God, and that, because of believing, you may have belief by means of his name" (v. 31). So, I'm kind of reluctant to concur with Bultmann when he evidently states that the Incarnation represents the focus of John's Gospel.