The Obvious Factor
There is a certain obvious factor with the heavens. The sky is needed for everything. It is from the sky the Sun's light reaches the earth and rain falls onto the Earth. Another obvious factor with the heaven's awe inspiring ability is its inaccessibility. Caves are explorable and mountains are climbable. But no matter how high you climb or build you cannot reach the heavens.
God Lives Up There
The word "Heaven" comes from the Old English word "heofen" meaning "place where God lives." Back in the days of the story Beowulf it also meant "sky." The idea of God living in the sky was well ingrained in Judeo-Christian thought with passage like Jacob seeing the gate of heaven as the gate to God's home (Genesis 28:17) and God saying he is speaking from Heaven (Exodus 20:22).
Ancient man did not have the ability to fly so the sky and heavens were seen as unattainable. To attempt to gain access by oneself and not via God was seen as a prime example of man's vanity. The Tower of Babel, E-sag-ila, was meant to be a monument to man's conquest of the heavens according to Genesis 11:1-9. The pseudepigrapha Book of 3 Baruch (3:5-8) tells of how the builders pondered about the very substance of the universe and wanted to see for themselves. God shut down the building fast. Combining this with the hardness of salvation and the sky became a very exclusive club.
The massive sky served as the throne of God. The heavens majesty and inaccessibility awed humans and reminded them of their puniness in the universe. Truly the geography of the cosmos played roles in the Judeo-Christian outlook.
This series will continue in more dispersed, minor posts.