In his massive new The Gospel of John: A Commentary (115-6), Frederick Dale Bruner has this to say about Jesus’ promise to Nethaniel in John 1:51.
He notes, first, that this is the first time Jesus speaks about Jesus; it is “Jesus’ first self-identification in a Gospel that is full of self-identifications.” That it closes the chapter that begins with the prologue on the Word is significant. The prologue ends with a declaration about seeing glory; the chapter ends with Jesus’ promise about seeing. What Jesus promises to show is, in context, the glory that John says “we” saw: An open heaven, angels ascending and descending on the Son of Man.
The structural link strengthens the notion that the heavenly ladder of the Son of Man is a temple image. Bruner is right: The end of John 1 “is almost as majestic as the multimembered prologue.” (We might note here that John’s gospel never shows us this; we need to add Revelation to the end of John to make it work. We also note that Bruner obscures the tabernacle connection by using Eugene Peterson’s unfortunate translation of John 1:14: “the Word became flesh and moved into the neighborhood.”)
Bruner helpfully emphasizes that the first of Jesus’ promises is to reveal an opened heaven. He notes, “The Church believes that among Jesus’ major contributions to history, and certainly to faith, is the gift of an opened and so somewhat demystified Heaven – an Opened heaven. Ever since Jesus, God is no longer only inscrutable mystery (though God always remains deep mystery). God has at last been ‘enfleshed’ . . . and wonderfully ‘exegeted’ . . . in the human life, Death, and Resurrection of Jesus, who is God’s autobiographical and substitutionary Word and Son.”