"In the beginning God created the Heaven and the Earth." Assume that creating the "Heaven" includes creating the "Heavenly host" = angels in that act. One of the angels created, named Lucifer, was described as the "son of the morning"
"How art thou fallen from heaven, O Lucifer, son of the morning! how art thou cut down to the ground, which didst weaken the nations!" (Isaiah 14:12).
The name "Lucifer" means, "Light bearer."
On the first Day as He creates the Heaven and Earth the other thing created that day was light, "Let there be Light." (Genesis 1:3)
The following passage describes Lucifer:
"..... You were the seal of perfection, full of wisdom and perfect in beauty. You were in Eden, the garden of God; every precious stone adorned you: carnelian, chrysolite and emerald, topaz, onyx and jasper, lapis lazuli, turquoise and beryl.Your settings and mountings were made of gold; on the day you were created they were prepared. You were anointed as a guardian cherub, for so I ordained you. You were on the holy mount of God; you walked among the fiery stones. You were blameless in your ways from the day you were created till wickedness was found in you. Through your widespread trade you were filled with violence, and you sinned. So I drove you in disgrace from the mount of God, and I expelled you, guardian cherub, from among the fiery stones. Your heart became proud on account of your beauty, and you corrupted your wisdom because of your splendor. So I threw you to the earth; I made a spectacle of you before kings. " (Ezekiel 28: 12-17)
Jesus Christ says: "I saw Satan fall like lightning from heaven." (Luke 10:18)
So to answer your question given that background, I believe Lucifer's job as the "Light bearer" was exactly that: the light bearer on Days 1, 2 and 3 of the Creation. On Day 4 God created the sun, moon and stars to mark the passage of time, supplanting Lucifer's role as the light bearer.
Lucifer became prideful in this pivotal role, and I suspect he was resentful that God did not keep him in that role.
As a created member of the heavenly host Lucifer's place was to serve the "Light of the World," the Creator, Jesus Christ in whatever capacity he was delegated to serve.
"Again Jesus spoke to them, saying, ‘I am the light of the world. Whoever follows me will never walk in darkness but will have the light of life.’ (John 8:12)
Lucifer wanted to supplant Christ's position as the "Light of the World" and he was thrown out of heavenly government for that mutiny.
FReegards!
