Why the sky? Jesus going up in the sky, heaven, etc.
We know now that the sky goes on seemingly forever, and that there is no mystical spirit world in the sky.
Why, then, are angels, Jesus, God, and heaven depicted as flying around or existing in the sky?
When Jesus died and resurrected, why the ascension into the sky? Wouldn't it make more sense for him to just pop out of existence and enter the spirit world?
There are some serious logical problems with all this flying around and living up in the clouds. I think the easy answer is that most pre-modern peoples believed that there really was some spirit world up in the sky, so their religious traditions reflected that premise.
This, I propose, is why they cared so much about astronomy and astrology.
REDUCTIO AD ABSURDUM.