Here is one I found:
The next three verses provide an answer to Nicodemus’s perplexity and doubt and also expand the Christological significance of the Gospel. In the ancient world there were many tales, such as in Homer or Virgil, of humans journeying to the remote places of the world and encountering mythological figures who reputedly affected the destinies of humans. Moreover, in the late formulations of the Gnostics there are numerous mythological explanations of an alien messenger visiting the realm of the cosmos to provide knowledge for the devotees concerning their origin and to remind them that they had suffered forgetfulness through a tragic error of a subgod like Sophia, who strayed from her natural relationships and caused the creation of the mundane world in which we exist.
The descent of the Son of Man here (3:13), however, is not like the mythological journeys of the ancient Hellenistic heroes or the mythological formulations of the Gnostics. The text here is rooted in an affirmation that the heavenly realities (3:12) are being opened to humanity because the divine Son of Man descended (katabas) into history! The aorist tense is intended to enunciate an event in history quite unlike any concept of the Son of Man in Enoch (68:2–6) or Daniel (7:14). The descent here obviously picks up the theme of a preexistent Son of Man in those earlier Jewish texts, but the descent and ascent of the Son of Man in John is clearly unlike anything in Jewish or Hellenistic literature.35 This descent of Jesus, the Son of Man, involved Jesus actually becoming human (“flesh,” sarx, John 1:14), an idea totally rejected by the later Gnostics and, although hinted at in texts like Isaiah 53, actually missed by Jewish interpreters. Indeed, it was hardly understood by Jesus’ own disciples—until after the resurrection!
This combination of ascent and descent is part of the great Christological formulation concerning Jesus, whom John knew had come to earth from heaven (ek tou ouranou), lived, died, was raised, and is once again with God in heaven. To understand about heavenly realities (epourania), therefore, the God-given means is through “no one but the one” (ei mē ho; translations like the NIV break the expression for ease of English) who has descended from heaven (3:13). For John, with his postresurrection perspective, the Christian gospel was the only way to salvation because Jesus alone descended and “has ascended” (anabebēken) to heaven.36 He knew the whole incarnational story when he started writing.
