Studying the world of Johannine Literature means partaking heavily in the scholarship of Raymond Brown. As my professor would say--This is the sea of Ray Brown, and we're just coming for a swim in it.
One of my favorite insights of Ray Brown would be the following, taken from his book The Community of the Beloved Disciple. Some background info: It is believed that there was a community which produced the Johannine writings. The functioned almost like a separate denomination, in modern terms. At some point, this community dissolved and many of its members and some of its writings were accepted into the larger Christian community--the community through which the New Testament was compiled and the Nicene Creed formed, and from which most modern denominations can trace their roots. Here's the quote:
"What I do want to reflect upon is the results for the Great Church of the amalgamation of the Johannine Christians into its membership and of the acceptance of the Johannine writings into the canon of Scripture. At various times I have referred to the theology of the Fourth Gospel as challengingly different, volatile, dangerous, and as the most adventuresome in the New Testament . . .
The ultimate check upon what Kysar calls the "maverick Gospel" has been the church's hermeneutical decision to place it in the same canon as Mark, Matthew, and Luke, Gospels which implicitly advocate the side opposite to many Johannine positions. This means that the Great Church, "the church catholic" of Ignatian language, whether consciously or unconsciously, has chosen to live with tension.
Tension is not so easily accepted in ordinary life, and we usually try to resolve it. So too in church history--but because of the church decision about the canon, attempts at simple resolutions of these theological tensions into a static position on one side or the other are unfaithful to the whole New Testament."
In Introduction the the New Testament, he makes a similar point:
"Divine providence furnished four different Gospels, not a harmonized version . . . Harmonization, instead of enriching, can impoverish."