Jesus appearing to them is a way of saying that it became so obvious that the Word of Christ was still alive, the spirit of Christ was supporting them and He was more alive in physical death than He had ever been, so alive that it was as real as if Jesus was in their presence made of flesh and bone.
Dead bodies do not come back to life and in the case of Jesus it was meaningless that His body return to live, the only part of Jesus that would reach across history to you was His Word and His spirit. That is what returned to life.
