Hey Astro. Welcome.

If you look at the account of the Transfiguration as a historical event then yes you have to explain how the disciples knew who Elijah and Moses were. But I agree with Porphyry. I think this episode in Mark is a literary invention, mostly because of the way it functions in Mark’s gospel. The episode is the center of gravity of the entire gospel. It simultaneously points back to the baptism and forward to the resurrection. It encapsulates every major theme of the gospel. Mark is presenting us with the figures of Elijah and Moses. He doesn’t have to explain. Luke and Matthew copied Mark.

So you’re clever enough to know it was a literary invention but you can’t think of a way to explain how Peter knew?

Thinking of such an explanation would be simple, but then I would be writing my own story and not reading Mark’s. Mark provides no explanation. He presents Elijah and Moses as he does Jesus transfigured and the disciples amazed. It’s a story not a newspaper report.

One could ask this question in terms of the degree of verisimilitude with which Mark is intending to achieve in his narrative.

I would agree with the idea of a kind of “dream logic” at work. But here I think Mark is aiming his narrative at the reader rather than concerning himself with internal consistency. He does this all through his gospel. “Breaking the fourth wall.” If we saw a contemporary painting of a figure labeled “St Elijah” no one would ask how the artist knows what Elijah looked like. Mark presents his audience with the figures of Moses and Elijah. Peter is “in the painting” not responding to it.