Irreparable harm is done to Christ and the Cross, when someone teaches that all will be saved eventually, even the Devil and his angels.
This makes Christ's suffering and death, meaningless.
MEANINGLESS!
The Devil and his angels cannot be saved, because salvation only takes place in the Body and is by faith. You cannot identify with Christ, be buried with Him in baptism and raised to newness of life as a spirit, You must have a body. Man sinned in the Body and that is why salvation must come in the body. After death, the judgment. If Jesus did not need a body ("A body thou hast prepared for me", Hebrews), and did not need to come and live victoriously as an overcomer in the body so that we could, also, then He would not have.
This man does not understand the propitiatory death of Christ and the relationship between sin in the body (through a person) and salvation in the body, (through a PERSON).
Christ has made no provision for those who sinned as spirits, angels.
The Devil has seen the Father and the Son, and spurned their rule over him. Therefore, he cannot have faith and will not repent. He is a liar and a deceiver and always will be. He cannot be trusted and proves that every day in his warfare against the Bride. He is not about to repent. He only lives to kill, steal and destroy. Are we going to believe Christ's estimation of him or some human's twisting of the Scriptures?
The rebellion that took place in heaven will never happen again. The only beings that are going to heaven are those who have been saved in the body and demonstrated true faith by a turning away from Satan, the flesh and the world and lovingly submitted to Christ. People who don't submit to the Christ, will be with the Devil and his angels.
Why has the Devil fought with Christ all these thousands of years? Where is his change of heart? According to Revelation, he is planning to destroy the Bride and then what, we all live happily ever after? Is Christ a deranged sadist? That is what Ultimate Reconciliation makes him out to be. It also makes Him out to be a fool, since there was no reason to die. Just force everyone to have a repentant heart and love you. That begs the question, when the Devil rebelled, why didn't the Lord offer him forgiveness right then and there and restore him rather than allow his onslaught against the Bride for thousands of years? Ultimate Reconciliation supporters ring hollow if they tell you that Christ is allowing the Devil to perfect the Church, because what is the mechanism for perfecting the Devil and conforming him to the image of Christ? Oh, God is just going to forgive him and this incredible act of love is going to change the Devil's heart and make him so grateful. Actually, the Devil will only see God as a fool, just another one that he deceived.
Ultimate reconciliation is a doctrine of devils.