My wife and I recently went to see the movie Sixth Sense, the basic premise is that ghosts do really exist and that the general reason ghosts exist is because they left something undone/unsaid before their death.
We had an interesting discussion during the trip home about whether ghosts really exist.
My take on the whole thing is this:
If even part of what I was taught at Sunday school is true, then the existence of ghosts isn’t too far of a stretch–so ghosts probably do exist. If you believe in: God, Creation, saints, miracles, stigmata, or the Apocalypse, then it logically follows that you believe in the human soul. If the soul of a human is such a powerful thing that it can give meaning and purpose to a pile of organic chemicals, then that same soul could easily hang around for a while independently of the body it once animated.
If you believe the teachings of the Bible, the existence of ghosts is a forgone conclusion… just take a look at Lazarus and several others stories that describe the animation of the dead or visits from the deceased.
As to the why ghosts exist, whether or not they have a purpose that they are trying to fulfill….
I’ll just have to leave that as an open question until I meet a ghost and ask it.