I found this topic fascinating. I'd like to share my understanding of the topic. Up front, I would like to disclose that I'm Catholic (I know, I know, nobody's perfect, right? lol).
These questions are fun questions to tickle the intellect and ponder theological possibilities. However, for some they are rather concerning, especially if one thinks they have encountered or are being harassed by some paranormal force. So, what I'm about to say isn't dogma, it's just one perspective. Even within the Catholic Church there are various interpretations of the matter.
I don't think any of us would question the existence of God, angels, and demons. So, I'll probably mention these only in passing if at all. I think the primary question is about what we call "ghosts" or the "disembodied spirits" of human beings. Up front, let's admit... demons can indeed appear as angels of light, loved one's, and even perhaps as a false Christ or God. But just because demons can do this it doesn't mean that ghosts cannot exist. After all, angels exist, and yet demons are said to be able to appear as angels of light.
But "ghosts"?
First, I think we should look to Sacred Scripture. Scripture does mention "ghosts" in my understanding:
- The Witch of Endor conjured the spirit of Samuel from the grave (1 Sam. 28:3–25).
- We are also told that Judas Maccabeus met the ghost of Onias the high priest in a vision (2 Macc. 15:11-17).
- The disciples thought Jesus himself was a ghost at one point (Matt. 14:26), indicating that they at least had an idea of ghosts and their possible existence.
- In the Gospel of Matthew, the disciples saw the spirits of Moses and Elijah with Jesus on the Mount of Transfiguration (Matt. 17:1–9).
- Appearing after his resurrection, rather than correct the very idea of ghosts, Jesus simply says he isn’t one (Luke 24:37-39).
Second, there is Sacred Tradition:
- The Church (I speak of the Catholic Church) has affirmed the numerous apparitions of deceased Saints as well as the messages they have brought to believers.
- Though theologians are divided on the issue, one of the greatest Doctors of the Church, St. Thomas Aquinas wrote about the belief in ghosts and apparently encountered a ghost on two separate occasions.
- The Church (the Catholic Church) affirms that a human soul who dies in "friendship with God", but has attachments to this life or the need of purification from venial sin, can experience a purgatorial state of existence as they work out letting go of these attachments or venial sins. These are considered to be "holy souls" who are ultimately destined for Heaven, only they are in need of some purification and help in letting go. The Catechism of the Catholic Church puts it like this:
All who die in God’s grace and friendship, but still imperfectly purified, are indeed assured of their eternal salvation; but after death they undergo purification, so as to achieve the holiness necessary to enter the joy of heaven (Catechism of the Catholic Church, 1030). . . . “purgatory … which is entirely different from the punishment of the damned”(Id., 1031).
- The Council of Trent (Fifth Session, 1563) made clear the Church’s doctrine on purgatory:
Therefore this holy Council commands the bishops to strive diligently that the sound doctrine of purgatory, handed down by the Holy Fathers and the sacred Councils, be believed by the faithful and that it be adhered to, taught and preached everywhere.
Personally, I believe that it is possible to encounter a "ghost". A genuine "ghost" would be a human soul that is caught in a purgatorial state of existence or a Saintly human soul appearing to bring a message or warning (but the latter are quite few and far between). God could also allow the soul of a loved one to appear to us in some form or fashion to reassure us of their salvation and bring us peace. Some "ghosts" might even appear to us in dreams.
A soul experiencing a purgatorial existence could be performing penance (this sort of "ghost" has been seen in some churches). Some "ghosts" could be emotionally attached to a place, action, person, or personal illusion in their own mind, and thereby find themselves unable to move on. Some might even be attached to this world through a sense of shock, denial, or need for justice.
Of course, only God is worthy of worship. However, if one encounters an angel one should certainly give reverence. Should one encounter a demonic spirit, I advise giving it wide berth and one should contact clergy to assist with the appropriate action. But if one is convinced they are dealing with a genuine "ghost" all one can do is pray for the soul.
It is a core teaching in the Church (the Catholic Church) that prayers be offered for souls experiencing what the Church has theologically termed "Purgatory". Remember, "Purgatory" isn't so much a place as it is a state of existence. Our prayers can lessen their suffering at the very least. However, the appropriate prayers and actions can even help these souls to let go of attachments to this world or the venial passions they are clinging to, thereby allowing them to become unshackled from their purgatorial suffering and move on into the beauty of Heaven and the very presence of God. Such prayers are found among various devotional practices and is even included in the Mass. I propose praying the Rosary with the stated intention of relieving the suffering of, and the setting at liberty, any disembodied human spirit in a state of Purgatory. If one isn't of the Catholic tradition one can certainly pray said intentions in their own words and perhaps even openly preach the gospel to them and encourage them to trust in God's grace and let go. Under no circumstances should communication be engaged in. This should be a form of prayer "ministry" for the deceased who are struggling.
Just offering an additional perspective to the conversation.
God bless.