# But they were terrified

"But" indicates a strong contrast. Jesus told them to be at peace, but they were very afraid instead.

# terrified and filled with fear

"startled and afraid." These two phrases mean about the same thing, and are used together to emphasize their fear. (See: [[rc://en/ta/man/jit/figs-doublet]])

# supposed that they saw a spirit

"thought that they were seeing a ghost." They did not yet truly understand that Jesus was really alive.

# a spirit

Here it refers to the spirit of a dead person.