Fellow Christians: Since nothing evil can be in Heaven, how was it that Lucifer could sin there?

Nothing evil can stay in heaven. I'm not sure the Bible teaches that "nothing evil can be in Heaven".

True, God opposes anything or anyone evil. He will have them cleared away at his proper time. But his time is not our own. 2 Peter 3:8 states as an example, one day with God is as a thousand years with us.

So it is that the assembly Jehovah God called for of all spirit creatures at Job 1&2, shows Satan coming in with the rest. Here Widely, Jehovah has made certain all heard Satan's rant, as well as Eve's claim for independence from Gods rulings pushed by Satan. This was Wisdom in action. Preventing any others from someday trying the same thing. God allotted time for those challenges to be settled. At his proper time, Jesus was made King of Gods Kingdom. His 1st action was kicking Satan & demons out if heaven. (Rev. 12:9, 12). Satan is angry with his travel limited as well as knowing he will die, comparatively soon.

So God will not tolerate any unrighteous behavior and will end it forcefully at the proper time. Not on our Human schedule.

You need to understand Jewish theology of the first century AD and before. In the non-canonical Second Book of Enoch, Third Heaven is described as a location "between corruptibility and incorruptibility" containing the Tree of Life. It also describes a Third Heaven as "a very terrible place" with "all manner of tortures" in which merciless angels torment "those who dishonour God, who on earth practice sin against nature." (chapter 10).

Other sources say it is were Adam is said to be buried, and where the garden of Eden is (or a perfect copy of the imperfect one that was originally on earth). It is mentioned by Paul in 2 Corinthians 12:2–4. It is where the dead go.

This is because they thought there were 7 heavens, with the upper being pure, and where death does not occur. The lower heavens is where Satan and his demons live.

free will

thats why he got booted out

right?

A person can better comprehend the mysteries of the afterlife by reciting daily and with care the angelic psalter of the Blessed Virgin.

his only sin is rebellion. he wants to be god himself. because of his marvels beauty.

Because God found quality and favor in him before he rebelled. He was an Angel, the scriptures tells us God made him in full beauty, lacking nothing. Now he sits there in chains, guarded by the Arch Angel Micheal until he is thrown out. God sentenced him to perish from with in, he will be consumed by fire from within his belly, after he has been set loose on the earth for a short season at the 6th trump, this is why he is also called the Son Of Perdition. that translated means "To Perish."

That would be an ecumenical matter.

because before he sinned he was not evil.

its like a criminal. before you broke the law you ere not considered a criminal

The ones who sinned aren't in heaven anymore. Angels have free will.