behold. Figure of speech Asterismos (App-6), for emphasis.
appeared. App-106.
Moses. Representing the Law, and those to be raised from the dead. See note on Matthew 8:4.
Elias. Elijah. Representing those "caught up" without dying. Both mentioned in Malachi 4:4; Malachi 4:5.
talking. talking together. In Luke 9:31 "they spake of His decease".