How could Lucifer have sinned? If he indeed was in God’s perfect presence then he would have been in perfect union. Eternal and perfect love, joy, peace and contentment would have been his and under these circumstances it is impossible to sin. Also, if it is true, then what’s to prevent other angels from sinning, or us when we go to heaven? Is it possible that Lucifer didn’t have perfect union?
God gave Lucifer a capacity of true free choice which involved the possibility of sin. It is possible for a being with free choice—even living in a perfect environment and without having some exterior temptation, such as Satan provided for Adam and Eve in the garden—to make a choice contrary to God’s will.
I agree it’s a mystery. Exactly how this can happen, I don’t know, but clearly it can. In order to have free choice the alternative of sin seems to be required.
However, an exception to this would be in our resurrected state on the New Earth where we are told there will be no more death and suffering. Since the wages of sin is death, the promise of no more death clearly means there will be no more sin.
I think we will still have free choice as resurrected beings but unlike Lucifer and Adam we will be covered by the blood of Christ and infused with his righteous character. That way we would no more choose sin than Jesus would choose.