Scholars have long considered the Gospel of John to be one of the latest written texts in the New Testament. The reasons for the conclusion that the Gospel of John was written after the letters of Paul, the Synoptic gospels (Matthew, Mark, and Luke), and many of the later letters, is based on a variety of evidences that when considered collectively suggest a post-90 AD composition.
Perhaps the most basic assumption regarding the date of composition of the Gospel of John is its theology in comparison to the other three gospels. Specifically, the fourth gospel emphasizes the divinity of Jesus and his premortal role as deity (John 1:1, 14). Jesus also appears to be omniscient in several episodes, such as the story of the woman at the well in Samaria, when Jesus knows intimate details concerning the woman’s marital status without being told them (John 4:16-18).
Jesus also declares that he is God in the Gospel of John (John 8:58) and associates Himself with Jehovah of the Old Testament. Other stories present a very exalted portrait of Jesus in comparison to the Gospel of Mark, for example, where Jesus appears to be angry (Mark 3:5) or where he appears to be “beside himself” (Mark 3:21). If theology and belief in Jesus developed from a more primitive understanding to a more exalted belief in Jesus as scholars suggest, then the Gospel of John is the end product of that development whereas the Gospel of Mark is the beginning.
A second leading factor in the discussion is that the Synoptic gospels are clearly in a conversation amongst themselves and they have in common roughly 90% of their material; whereas the Gospel of John can often be considered as a later commentary to that early conversation. An example of this occurrence may be found in the account of the Mount of Transfiguration, which the Gospel of John omits, by chance because the story was already recorded in three earlier sources. Many of John’s omissions can be interpreted in this way, even though the logic is clearly circular.
Another important consideration is that the Gospel of John may be trying to counteract certain break-off Christian groups, sometimes designated as Docetists, because of their belief that Jesus was not actually mortal, but instead, they advocate, Jesus only appeared to our eyes to be mortal.
John may have attempted to undermine these claims by including stories of Jesus eating fish (John 21:12-15) and that He was flesh and dwelt among us (John 1:14). The Docetic movement is dated by scholars to the last decades of the first century and then into the second century, which would place the time of writing for the Gospel of John contemporary with the rise of Docetism.
All of these considerations, including several others, are certainly subjective pronouncements that cannot be proved or disproved. The physical evidence for the Gospel of John is likewise inconclusive and therefore our only recourse is to consider the surviving literary evidence. As long as the scholarly model of theological development continues to hold sway, the Gospel of John will be considered a late first century document that captured one of the final theological statements of the first century church.
Scholarly caution mandates, however, that the late dating of the Gospel of John remain a tentative conclusion that is the result of a theory of Christian origins rather than a comprehensive literary theory used to explain the Gospel of John itself.