Did John Write John? The Evidence is Clear.
A common notion floating around in Pop Culture is that "modern scholarship" has somehow proven the Gospel of John is more or less unhistorical fantasy written by a pseudonymous author.
Here’s the facts: the tradition of the Church, supported by the unbroken line of patristic testimony, as well as internal evidence from the text itself, is that the gospel is rooted in the testimony of the Apostle John, son of Zebedee.
St. Irenaeus tells us (circa 180 A.D.) that the fourth gospel was published by the Apostle John, the teacher of his own mentor Polycarp. Numerous other witnesses in the second and third centuries corroborate this basic witness. In addition, various elements within the gospel strongly suggest John as the author. Most obviously, there is the attestation of the witnesses penning the gospel that it is the testimony of "the disciple whom Jesus loved" (John 21:24)—a disciple to whom no one but John corresponds. The source of the gospel is, quite clearly, a Jew familiar with the conditions of Palestinian Judaism at the time of Christ. He speaks Aramaic and Greek. He knows Jerusalem as it looked before Rome reduced it to rubble in 70 AD. And he gives countless details which, if they are not the testimony of a first-hand eyewitness who was present at the Last Supper, are an absolutely isolated occurrence of novelistic realism nineteen centuries ahead of its time. That he was part of Christ's "inner circle" of Peter, James and John (cf. Galatians 2:9) is even more likely given that he was the disciple at the Last Supper who laid his head on Christ's breast. He can't be Peter, who is distinguished from him in the text, and he can't be James (who died in the early 40s). So it all points to John.
Additionally, the patristic tradition that the gospel was composed in Ephesus also points to John. First, this is the city associated with the Assumption of the Virgin who was commended into his care. Second, the gospel repeatedly answers a sect devoted to John the Baptist with the reply that John “was not the Light” but had only come to “bear witness to the Light” (John 1:8). We know from Acts 18:24 and 19:1-7 that there was such a sect centered in Ephesus. Finally, the sophistication of the gospel fits the fact that the New Testament epistle with the most sophisticated exposition of theology is the epistle to the Ephesians.
Conclusion: all the evidence point to the accuracy of the Church’s tradition (noted by Irenaeus around 180 AD) that John published his gospel in Ephesus in the second half of the first century.
Some critics, eager to look for crack in this evidence, will note that the Greek of John’s gospel and epistles is of a different quality than the Greek of John’s Revelation and say, along with Eusebius, that Irenaeus might have had his Johns mixed up between multiple individuals. Others, grasping at straws, may claim that Mark 10:38-39…
But Jesus said to them, "You do not know what you are asking. Are you able to drink the cup that I drink, or to be baptized with the baptism with which I am baptized?" And they said to him, "We are able." And Jesus said to them, "The cup that I drink you will drink; and with the baptism with which I am baptized, you will be baptized.
…implies that both James and John suffered a martyr's death, contradicting John 21:22-23.
But these arguments are weak as well. To be sure, there is a strain of thought dating back to Eusebius that John the apostle and John the “elder” may be two different people. But so what? We know from internal evidence (John 21:24), that the gospel has more than one hand involved in its composition. Given the common use of an amanuensis (a secretary who took dictation) in the New Testament, that shouldn't surprise us. The editors of John make it abundantly clear that they have some sort of hand in the composition of the gospel, but that the gospel is nonetheless rooted in the testimony of the “beloved disciple” whom they know intimately.
This means the discrepancy in writing styles between the Gospel and the Revelation could be due to any number of factors. It may be that John wrote his gospel with the help of another person named John (then, as now, a common name). It may be that he had no amanuensis when he wrote his Revelation (which would explain the different styles and the difference in competence in Greek). None of this disproves the strong evidence that John bar-Zebedee is the source of the testimony in the gospel.
Likewise the attempt to pit Mark 10:38-39 against the testimony of John 21 is what happens when you let all your biblical interpretation be done by people who are on a single-minded mission to show that everything in the Bible is false, untrustworthy, etc. Such determined misreaders wind up forgetting that it's a human book using human language in their zeal to prove it's not God's book. So the critic sets himself the absurd task of insisting that it couldn't be possible Jesus is simply saying that James and John are going to endure suffering for his sake, or that the murder of James would be a bitter cup for his brother John to drink. No, they have to insist that Mark thinks John was martyred, even though the whole tradition of the Church preserves no such tradition at all. One hears the sound of an ax on the grinding wheel of an agenda, not of a sensible reading of a text.
And that's just the beginning. More next time...