Christians believe in being born again (accepting God, following God's laws). That means that one can not believe at one time, and believe at another. I suppose the opposite is true, as well (a person who believes in Christianity could suddenly lose faith).
Lucifer used to be an angel, but later became bad.
Young children who die go to heaven, but as they learn, in heaven, they might become corrupt and be evicted from heaven. I wonder if the same is true of adult angels?
I don't believe things work the way scriptures say they do. I think that God is made of billions of souls, and almost all are good, but some are bad. I think that God puts a tiny piece of himself in each of us (except those few without souls), and that soul guides our evolved monkey-like body to do good or bad. Of course bad souls go to hell, and good souls go to heaven. Free will is necessary to make sure that the goodness or badness of the soul guides it to heaven or hell. All this, in my opinion, is a purification system for God.
Pastors would throw a fit if anyone suggests that God is anything but pure good. Yet, look at what God allows.....Satan, pain, death, death of Jesus, animals preying on other animals, stink, etc. Would a purely good God make us flawed humans then blame us for being flawed and kick us out of Eden, flood the world, and destroy sinful cities?
But, if I am right, and the soul guides us, is it possible to make a bad soul good? Apparently goodness can be learned.
Similarly, badness can be induced by temptation with fear and lies. Take for example, God's commandment "thou shalt not kill." When attacked by al Qaeda terrorists, we should have followed God's laws "turn the other cheek" "not kill," but, instead, the country of Iraq (which, as it turned out, was innocent of terrorism), was attacked in our lifetime (twice...once by the dragon and once by the beast, as predicted in Revelation), and fear of future terrorist attacks tempted us into defying God (a very great sin that resulted in COVID (Revelation 15), and eventually God will destroy all life on earth.
W. Bush issued phony orange alerts to get citizens of America to attack North Korea (though at the time, it was a peaceful nation). Tom Ridge, director of Homeland Security, was the only one who had authority to issue such alerts, and he said that the alerts didn't come from him, but did come from his superiors (that would be President W. Bush and VP Dick Cheney). So, it is Satan's fear and deception that prompted war in defiance of God's commands.
By using Satan's fear and deception, good souls can be corrupted to go to hell instead of heaven.