In a previous post, I have tried to make a case (thoroughly unoriginal) for the apostle John as the author of the Gospel that bears his name. Assuming John wrote the Gospel, why did he write it? The best place to start is with his own purpose statement in John 20:30–31: “But these [signs] are written that you may believe that Jesus is the Messiah, the Son of God, and that by believing you may have life in his name.” John selected several startling signs of Jesus (seven, I believe; see my BBR article cited below) to convince his readers that Jesus was in fact the promised Messiah (or, as Don Carson has it, that the Messiah was in fact Jesus). His purpose was to induce his readers (or those with whom his readers came into contact) to believe in Jesus and thus have life in him.
John, therefore, was possessed by a holy focus. This is not an autobiography, or even a biography (a “life”) of Jesus. Rather, John’s Gospel is an aid to personal faith. So much for the purpose. Now what about the occasion?
This may be harder to determine. Certainly tradition seems credible that John at the urging of some of his disciples wrote his Gospel toward the end of his life (Clement of Alexandria, cited by Eusebius, H.E. 6.14.7). But what were the circumstances surrounding John’s writing? And were there other purposes that guided him as he penned his Gospel?
In a recently published article, I have argued that the destruction of the Second Temple in A.D. 70 may be an important external historical datum for the composition of the Fourth Gospel. No one disputes that the temple was destroyed in A.D. 70, and clearly this was a momentous event with far-reaching consequences, and very few Johannine scholars question that John’s Gospel was written subsequent to A.D. 70 (most opt for the A.D. 80s or early 90s). So it seems natural to draw a connection between the destruction of the temple and the writing of John’s Gospel. Internal evidence seems to confirm this. Throughout the Gospel Jesus is presented as the fulfillment, and hence replacement, of all kinds of Jewish festivals and institutions, including the temple (see esp. 2:13–22).
Peter Walker, in his important book Jesus and the Holy City (Eerdmans, 1996, p. 197), says it well: “As a result, if any of his readers felt bereft of the Temple and of the spiritual focus provided by Jerusalem, John would have encouraged them not to mourn the loss of the city, but rather to see what God had done for them in Jesus. . . . The Evangelist, writing after the Temple’s destruction, does not bemoan its loss. . . . The presence of God has not been withdrawn, for Jesus has taken the place of the Temple. Jesus gives more than the Temple had ever given. . . . Jesus stands in the place of everything that Israel has lost.”
For further study see my essay “The Destruction of the SecondTemple and the Composition of the Fourth Gospel, ” TrinJ 26NS (2005): 205–42, with ample references to the burgeoning literature on the temple theme in John’s Gospel and research on the Second Temple and its destruction; as well as my book A Theology of John’s Gospel & Letters (BTNT; Zondervan, 2009). See also D. A. Carson, “Syntactical and Text-Critical Observations on John 20:30–31,” JBL 124/4 (2005): 693–714 and my article “The Seventh Johannine Sign,” BBR 5 (1995): 87–103.