The notion of ascension (to heaven) is a product of the apocalyptic era, beginning roughly around the third century BCE with the First Book of Enoch. Apocalyptic literature generally follows the appearance of an Israelite hero transported to heaven, given instructions on what is soon to follow, and returned back to earth to report the news. Enoch was a perfect candidate because, as recorded in Genesis 5:24, “Enoch walked with God; then he was not more, because God took him, meaning he went to heaven without experiencing death. Situated there, he is a convenient reporter.
Jesus’ ascension was, according to Luke-Acts, a public, visible event. …as they were watching, he was lifted up, and a cloud took him out of their sight. While he was going and they were gazing up towards heaven, suddenly two men in white robes stood by them. They said, ‘Men of Galilee, why do you stand looking up towards heaven? This Jesus, who has been taken up from you into heaven, will come in the same way as you saw him go into heaven.’ This is depicted in starkly literal terms: watching, lifted up, while he was going, will come in the same way you saw him go into heaven. Why is such literal detail employed? I believe it has to do with verifying a literal, bodily resurrection.
Here’s how. Since Jesus is depicted in all the gospels as lingering on earth with the disciples following the resurrection, conversing, eating, teaching, etc., and Jesus is now in an eternal state where he will never die, somehow his body must be removed from the earthly scene. John’s motive is that Jesus cannot be with everyone simultaneously if he lingers, so he is replaced on earth with the Comforter. This also fulfills the apocalyptic yearning for the Messiah to return to earth to inaugurate the kingdom of God.
But, something is amiss. For Jesus to literally ascend to heaven, that is, leave the earth and ascend through the heavens (atmosphere and heavenly bodies), heaven must be above the earth. In other words, this could only be envisioned in the ancient cosmology of the three-tiered universe. In the universe, as we know it, this could not happen. Therefore, it is a patently made-up event.