They were startled and frightened, thinking they saw a ghost.
Luke 24:37 (NIV)
This incident shows that the disciples were afraid of an apparition.They thought that they saw a ghost.
A ghost is 'the spirit of a dead person, especially one that is believed to appear to the living in bodily form or to haunt specific locations (American Heritage® Dictionary of the English Language, Fifth Edition).
What does Evangelical Presbyterians believe about ghosts?
Once upon a time the word 'ghost' was synonymous with 'spirit'. Every person had a 'ghost', and their 'ghost' went to be with God when they died. This is why the Holy Spirit is sometimes called the Holy Ghost, and where we get expressions like "give up the ghost'. In that sense virtually all Christians believe in the existence of ghosts, meaning that all people have a spirit.
Today the word 'ghost' specifically means a disembodied spirit that haunts people or places. In that sense, there are no Christian denominations that require members to believe in ghosts. Since there are bible passages that refer to people returning from the dead, most biblical literalists believe in at least the theoretical possibility of disembodied spirits appearing on earth, but that is a long way from believe that all or most reported hauntings are real.
Practically this means that in any Christian denomination there will be some people who believe in ghosts, and some who don't.
According to Tommy Phillips, the pastor of Watermark, a C&MA church in Tampa, FL (a branch of Evangelical Presbyterians), the disciples assume the figure is a ghost because water is an extension of the Abyss.
As he explains in his series starting in Genesis, all throughout the Old Testament, water is associated with the Abyss, and subsequently associated with the unknown, the underworld, with chaos and destruction. The Abyss is in place prior to the creation of the world, and is a recurring instrument of destruction in the Old Testament narrative. Flood destroys the world, God holds back the Red Sea for the Israelites but drowns the Egyptians, Nehemiah being told to submerge himself, Jonah being tossed overboard, etc., all the way up to the introduction of Jesus. The concept of voluntary baptism, the demon-possessed pigs running into the river, and this specific passage where they see someone walking on water, and they immediately think it is a ghost, is mentioned.
I can't link an article, as the sermon is online only as a series of podcasts.
