The Gospels were written for a particular audience, addressing particular needs, for a particular church community, at a particular time in history. These same Gospels must speak to us today, in our particular time and address our particular needs, facing situations in the 21st cent not envisioned by the early writers. Scripture is a living reality, not a dead book, and as John promised,
The Paraclete is "the Spirit of Truth" who supplies guidance along the way of all truth (16:13). The Johannine Jesus had many things to say that his disciples could never understand in his lifetime (16:12); but then the Paraclete comes and takes those things and declares them (16:15).
The evangelist does not lose faith in the second coming but emphasizes that many of the features associated with it are already realities of Christian life (judgment, divine sonship, eternal life). And in a very real way Jesus has come back during the lifetime of his companions, for he has come in and through the Paraclete. The Johannine Christians need not live with their eyes constantly straining toward the heavens from which the Son of Man is to come; for, as the Paraclete, Jesus is present within all believers: their Advocate, their Consoler, their Guide to all truth.