Albert Barnes Commentary Matthew 17:3

"And behold, there appeared unto them Moses and Elijah talking with him." — Matthew 17:3 (ASV)

And, behold, there appeared unto them Moses and Elias. Moses was a distinguished servant of God, through whom the law was given, and whose institutions prefigured the Messiah. It was particularly fitting that he should appear when his prophecies and types were about to be fulfilled, and his rites to be ended.

Elias, or Elijah, was a distinguished prophet, taken to heaven without experiencing death (see 2 Kings 2:11). Elijah had been eminently honored by being translated in this way, and even more by being made the model for the forerunner of the Messiah (Matthew 11:14; Luke 1:17). They appeared in glory (Luke 9:31), that is, as they are in heaven—with the glory that the redeemed have there.

Talking with him.Luke 9:31 informs us that they conversed about his death, which he was to accomplish at Jerusalem. To redeemed spirits, that death was an object of intense interest. By faith in that death they had been saved; and now that the Redeemer of mankind was about to die, it is no wonder that this was the focus of his and their thoughts.

Luke adds (Luke 9:32) that Peter and those who were with him were heavy with sleep. It is likely that this occurred at night, that Jesus was engaged in prayer, and that he had permitted his weary followers to rest. It was after they were awakened that they saw this vision. Probably the sudden splendor, the bright shining, aroused them from their sleep.