Mark 9:2–9 (CEB)
Six days later Jesus took Peter, James, and John, and brought them to the top of a very high mountain where they were alone. He was transformed in front of them, and his clothes were amazingly bright, brighter than if they had been bleached white. Elijah and Moses appeared and were talking with Jesus. Peter reacted to all of this by saying to Jesus, “Rabbi, it’s good that we’re here. Let’s make three shrines — one for you, one for Moses, and one for Elijah.” He said this because he didn’t know how to respond, for the three of them were terrified.
Then a cloud overshadowed them, and a voice spoke from the cloud, “This is my Son, whom I dearly love. Listen to him!” Suddenly, looking around, they no longer saw anyone with them except Jesus.
As they were coming down the mountain, he ordered them not to tell anyone what they had seen until after the Human One had risen from the dead.
In the eighth chapter of Mark, right before today’s Lectionary passage, Jesus asks the disciples who he is, and Peter answers “‘You are the Christ,” but then Jesus tells the disciples he will be rejected by the religious leaders, and then killed, and then rise from the dead.
The disciples don’t know how to take this — obviously, given their reactions when it happened, they didn’t quite understand it or take it too literally. Peter scolded Jesus for saying such a thing, and that’s when Jesus scolded Peter, with the famous phrase, “Get behind me, Satan.”
Now, about a week later — Mark says six days later, Luke says eight days later — Jesus takes the three disciples who were closest to him and goes up onto a high mountain. The Bible does not identify the mountain.
Starting in about the Third Century, church tradition held that it was Mount Tabor, and there’s a Catholic church on Mount Tabor called the Church of the Transfiguration.