How did Peter, James, and John recognize Moses and Elias (Elijah) at the Transfiguration (Matt. 17:1-8; Mark 9:2-8; Luke 9:28-36)? No iPhone pics were sent in those days!
So true! Since it doesn't seem likely that they introduced themselves when they appeared, how would the apostles have figured out that it was Moses and Elijah? Scholars mostly appeal to the idea of tradition, but don't agree on what that tradition really said.
For a while, it was fashionable to say that Moses and Elijah appeared as representatives of the Law and the Prophets. The problem, of course, is that in addition to being a lawgiver, Moses was also considered to be a prophet. And although Elijah was a prophet, he would hardly be representative of the prophetic tradition. Given the major writing prophets of later centuries like Isaiah and Jeremiah, Elijah's name is not the first one that comes to mind when one thinks of the prophets. So this theory has largely fallen out of fav
Another option is that neither of them actually died. Elijah was "translated" – taken up to heaven in a whirlwind. And Moses – well, no one ever saw him dead. Legend has it that he was buried by God. (But then that raises the problem of Enoch who also "walked with God.") However, the fact that neither Moses nor Elijah died does not seem to have any relevance to the Transfiguration story.
Some scholars think they were chosen because they were great wonder-workers in the Old Testament or because they were both elder statesmen. But even then, these same scholars admit others also did miracles and that Elijah doesn't seem to fit the "elder statesman" role. It is true that they were both deliverers – Moses delivered the Israelites from Pharaoh, and Elijah delivered the people from the Baal prophets. While Moses' role was a defining moment for the Israelites, it's hard to say the same for Elijah -- especially in light of people like Joseph, Joshua, and David, who were also great deliverers.
On the other hand, all of the Synoptic gospels connect Moses to Jesus in various ways. In Jesus' day, tradition held that some day God "would raise up a prophet like Moses" (Deut. 18:15). Jesus' followers took great pains to show that Jesus was that prophet. He would lead the people just as Moses had led them in an earlier time. Jesus did usher in a whole new way of understanding God. Elijah was the prophet most associated with the final days. Malachi declared that God would one day "send you Elijah the prophet before the coming of the great and dreadful day of the Lord" (4:5).
So, in the persons of Moses and Elijah, readers are reminded of their great history, as well as their future when God's promise will be fulfilled. Maybe their presence was interpreted as a sign that the final "Day of the Lord" was about to occur – but it didn't.
Scholars have no trouble with the fact that both of them appeared. In a sense, scholars might say that Jesus brought the work of Moses and Elijah to completion. Together, they function as witnesses from the OT on Jesus' behalf. Both Moses and Elijah met God on Mount Sinai (Horeb). The Transfiguration occurred on a mountain. It certainly gives credence to Jesus' ministry and mission.
Lastly, readers should consider the simple explanation that if God caused Moses and Elijah to appear, he also caused the disciples to know who they were. No introductions were needed!