This is because we need to be clear what is meant by the word 'ghost'. It is true that there is a 'spiritual dimension' to the universe in which spiritual beings exist. These beings are either good or evil; they are either obedient to God or they are in rebellion against him (Ephesians 6:12). These spiritual beings can manifest themselves in the world, and we often refer to them by the general terms 'angels' and 'demons' (for more on angels, read the Advent 2019 reflections on this blog). The difficulty comes because evil spiritual beings don't mind lying – they will masquerade as good angels (2 Corinthians 11:14) or even as deceased people.
The term 'ghost' usually refers to the 'souls' or 'spirits' of people who have died, which can appear and even communicate with those who are still living. Thus they are thought to be human rather than spiritual in origin (this is further confused by the common but incorrect view that we become angels when we die). However, there is no such 'limbo' state: “people are destined to die once, and after that to face judgment” (Hebrews 9:27). Jesus tells us (Matthew 25:31-46) that judgment leads either to an eternity in the presence of God or an eternity cut off from God's presence (which therefore cannot be in the world as God is present in the world). And Jesus' physical resurrection from the dead teaches us that our resurrection will also be physical – he even told his disciples “I am not a ghost!” (Luke 24:39). Humans are 'embodied souls' and 'ensouled bodies' (Genesis 2:7) - the two cannot be separated, that is why Paul teaches that at our resurrection we will receive immortal bodies (1 Corinthians 15:53).
So do ghosts exist? If you mean 'do the spirits of dead people hang around in the world?' then the answer is no. Some might point to mediums who have told them things that were only known by themselves and the loved one as proof that this is indeed the spirit of the dead person communicating. It may be true that no human could know those things but as these beings are supernatural, they have knowledge that humans don't. The medium may indeed be communicating with spiritual beings, but these beings are impersonating humans and must therefore be evil, as God has forbids us from trying to contact the dead (e.g. Leviticus 19:31, Deuteronomy 18:9-12).
Halloween is a time when evil spiritual beings are trivialised and rational people will claim to have seen ghosts or communicated with dead loved ones. There is only one person who has spoken to us after their death, the physically resurrected Jesus, and one of his messages to us is “stop doubting and believe” (John 20:27).
