There are so many moments in the gospels when what we read seems less like a factual narrative account of the activity of Jesus and his followers and instead is more like an attempt to frame and present -- sometimes fantastically -- a necessary theological claim.
One of those is when we read at the end of the Luke's gospel the story of Jesus ascending into heaven to be at God's right hand. There are several pieces that come together to make His ascension the "preferred method" for Luke to end Jesus' resurrected time on earth.
That Jesus "born of the virgin Mary" was fully human is as good a place to start as any. And as fantastic as are the stories of angelic visitations and announcements, and shepherds, along with Matthew's stars, and dreams, and wisemen we hold fast to the claim that he was born into the world of time and space as humans are born. When Jesus dies it is the end of a human life, horribly ended but human nonetheless. Time and space cannot be ignored.
That God raised Jesus from the dead is another claim that makes ascension theologically necessary. And it is important to remember that resurrection cannot be less than incarnation. It can be more, however.
It is more. Luke's description of Jesus as appearing but unrecognized on the road to Emmaus and then disappearing at dinner is a fairly modest attempt to account for the difference that resurrection made to this "human one." It is similar to John's treatment of Jesus as capable of passing through locked doors and yet still possessing just as much of a body as was the one crucified. A body that Thomas is able to touch.
The 40 day thing is also necessary and functions as a literary device similar to its previous use when Jesus is driven into the wilderness. It marks a completed period of paradigmatic change. Just like the children of Israel were changed in their 40 year wilderness sojourn and the earth was cleansed by forty days and nights of rain, in this case Jesus' "work" is done.
Another way to say it is that resurrection is NOT resuscitation, so when his work is complete, dying is no longer an option for Jesus. The "best" way for him to get to heaven is to just go there. And that's what he does: "he withdrew from them and was carried up into heaven." (Luke 24:51)
It is a modern yet sophistic curiosity that puzzles about the location of heaven, his direction and rate of ascent, etc. So we can get back to more necessary theologies we should admit that if Jesus was removed at the speed of light he'd still be within the bounds of what we call the Milky Way. Better to give God credit for something other than attaining warp speed.
Obviously, Jesus' rate of ascent was not Luke's point. What was important for Luke was to have us understand that God had done EVERYTHING that was necessary to be done: life, death, resurrection, and ascension; all necessary and all from God.
Pentecost is the next necessity.
Pentecost is the next necessity.