Your mission, should you decide to accept it …
The question is: Does God send souls in Heaven back to earth to serve His purpose?
I think the best way to answer this is by analysing things step by step.
What happens to us when we die?
Two schools of thoughts. Some believe we come face-to-face with God and we are judged and we go to either Heaven or hell. Catholics also believe we go to Purgatory; but let us not complicate matters even more for now. The options, according to some, are Heaven or hell. Others believe that we wait for Judgement day, (whenever that is), when all will rise and be judged. If the latter is the case, then where are all the souls who have died over the centuries past? There must be millions and millions of them. Are they in a waiting-room somewhere reading out-of-date newspapers and magazines?
When Christ died on the Cross He said to the thief by His side, "Today you will be in Paradise with me". He did not say, "but you have to wait for Judgement day, whenever that is!" or "but you will have to spend time in Purgatory first!" He said, "today"; implying instant judgement at the time of death.
When our loved ones die, often at the funeral we are told in sermons that they are in Heaven, looking down on us. We are not told they are waiting somewhere.
All this implies that we are judged at the time of death and our "destination" is decided upon then.
That being the case, what happens to all those souls in Heaven? Are they there for eternity with God? Or are they somehow asked to serve God's purpose in some way?
When Christ went up the mountain with Peter, James and John, (The Transfiguration - Matthew 17:1–8, Mark 9:2–8, Luke 9:28–36), the disciples saw Moses and Elijah talking to Jesus. Now we assume that they saw them as bodies not just spirits. This means that God is able to let dead people appear again on earth as human bodies to suit His purposes.
So the question is: If God wanted to, can He allow a certain dead person to go back to earth to serve God's purpose? The answer is YES - God can do anything. The next question then is: Does God do that? Does He send people, (souls), back to earth to serve His purpose? We don't know the answer, but I see no reason why He does not do so.
God sent Angels many times on earth to announce to Mary about Christ's birth, to announce to the shepherds the same thing, and to warn Joseph to go to Egypt. So why can He not send souls from Heaven to visit earth to serve His purpose - perhaps to protect us? In fact, this raises the question: Are Angels souls of those who have died and gone to Heaven? Do souls in Heaven somehow become Angels?
Whilst we have no answer to those questions, and they are not raised in the Bible, apart from the fact that Angels exist, we can assume that if God wanted to He could make souls in Heaven Angels, and He could send them to various missions on earth.
So whilst we are at it and assuming; let me go off at various tangents simultaneously.
What/who are ghosts?
When Christ walked on water, His disciples on the boat thought they had seen a ghost. Jesus did not say, "Hold on chaps. There are no such things as ghosts!"
When He appeared to the Disciples after the Resurrection, He said, "Look, it is me. I am not a ghost. I have flesh and bones. Ghosts do not have flesh and bones". (Luke 24:36 onwards - and other Gospels).
So this implies that ghosts do exist and they are spirits - not humans with flesh and bones. The question then follows: What/who are ghosts? Are they souls sent by God from Heaven for a special mission? Are they Angels - and we have named them ghosts for want of another description?
Or are they demons?
We know from the Bible that the devil was at one point an Angel who rebelled against God. He, and presumably other followers, left Heaven and became devils/demons. But are these the only devils in existence? Or are their numbers added to over the years from souls that go to hell?
Again, we have no Biblical answer to this, and our guesses are just that - guesses surmised from our imagination and beliefs.
Suffice it to say that we know, from Bible readings, that:
God can allow dead people to appear again on earth as humans with flesh and bones - Moses and Elijah at The Transfiguration.
Angels do exist - several Gospel mentions.
Ghosts do exist - two Bible mentions referred to above.
Devils do exist - several Bible mentions.
Whether any of the above are souls of people in Heaven, (or hell), who are allowed to return to earth for special missions, I am afraid will be one of those unanswered questions that will puzzle us and future generations.
So, to answer the question: Does God send souls in Heaven back to earth to serve His purpose?
In all honesty, I don't see why not? Why would God not send a loved one who has died back to us as an unseen spirit to protect us from evil? I know many people believe this is so. I think I do. I know that God can do this if He wishes; so it is probable/possible that Angels are such souls who have pleased Him in Heaven and are sent with special missions to protect us.
I believe we all have Guardian Angels. I believe we can pray to Saints and ask them to pray for us and seek our protection. What are Saints after all? Are they not dead people who are in Heaven and have pleased God in their earthly missions? Can we not all be Saints - one day?