Obi - Wan tells Luke that he must face Vader again in order to save the galaxy .
Luke then learns from Obi - Wan 's spirit that he has a twin sister , whom he immediately realizes is Leia .
Obi - Wan tells Luke that Luke must face Vader again in order to save the galaxy .
Luke then learns from Obi - Wan 's spirit that he has a twin sister , whom he immediately realizes is Leia .