Lucifer's Sin.

https://en.wikipedia.org/wiki/Theft_of_fire

The element of fire in classical philosophy represents an energy that is an activating and purifying energy, often associated and corresponding to spirituality. Without the element of fire, we wouldn't have a spirit, without the element of fire, we wouldn't have life. We wouldn't have forethought, the ability to take action, we would be just like animals.

The classical elements can be thought of as psychological energy which composes the psychological realm and the spiritual realm, water represents emotions, air is intellect/mind, and fire is a purifying activating energy which composes a lot of what we would deem as spirit but some philosophers believe in a 5th element as "spirit", all of these elements in different combinations make up the spiritual and psychological realm.

Fire is associated with strength, activity, blood, and life-force. It is also seen as highly purifying and protective, consuming impurities and driving back the darkness.

Fire is traditionally seen as the most rarefied and spiritual of the physical elements because of its masculine properties (which were superior to female properties). It also lacks physical existence, produces light, and has a transformative power when it comes in contact with more physical material.

https://www.learnreligions.com/elemental-symbols-4122788

With the fire came the ability to create, just as God created man, man then created psychological symbols and God's to represent spiritual truth. When we previously lived on darkness, we then had the ability to shine light on it and discover higher spiritual truths.

Lucifer, meaning the light bringer gave us life, and in response we demonized them.

Without Lucifer, we wouldn't have the ability to enter the Kingdom of Heaven.

Pometheus is a Luciferian figure, a God that typically corresponds to Lucifer. In regards to fallen angels in the book of Enoch, their sin was coming down to teach humans knowledge.

If you want to know his actual sin, it was being responsible for giving humans forethought by stealing the power of creation from the God(s) and giving them to man. It wasn't pride, and the rebellion was more of angels choosing to leave heaven on their own volition. They weren't stuck there, they could leave.