If you have ever read the Gospel of John you will notice that he talks a great deal about up and down,light and dark.
John believed that all good belonged to God and as such resided upwardly and all evil belonged to the other guy,or satan and was earthly,lower and downward.
In John 3:14 he says"And As Moses lifted up the serpent in the wilderness,even so must the son of man (Jesus),be lifted up".
Jesus started out in the heavens but came down to earth in a form we could understand,that of a man.Basically he physically lowered himself to our level of understanding.
In the story of Moses in the desert, he lifted the serpent up so the people who were being attacked by burning serpents could see the serpent and be healed,from what I understand the snake represented sin and spiritual death being lifted up toward God for forgiveness.
The serpent started out in a downward position and was raised upward.Jesus on the other hand started out in an upward,holy position and was brought downward to our level.
When Jesus was crucified his cross was lifted upward and Jesus hung between the heavens and the earth,like the holy spirit hung over the water when God created the earth.
Jesus became the embodiment of the snake being lifted up with all our sins attached to him so we could be no longer spiritually dead.
After his Resurrection he Ascended and was lifted up into the heavens to again reign over us.
In our faith we are to look up and be lifted up toward God.
That is why we are called the light of the world because light in nature is found in the skies not in the ground.