I am always intrigued when Luke changes a detail in a story that he found in Mark, which he used as a source. Mark says that the transfiguration occurs six days after the previous scene—the account of Peter's confession that Jesus is the messiah and Jesus' first passion prediction. Luke changes the timeline to say that the transfiguration occurred "about eight days" later. If he goes to the effort to make a change, there must be a reason for it. Why might eight days be significant?
One possibility is that an eighth day marks the beginning of a new week. Some see the transfiguration to be a foreshadowing of the resurrection. The resurrection occurred on the first day of the week, which would be the eighth day, the beginning of new creation. Just as the transfiguration gave the disciples a foretaste of the resurrection, so the resurrection gives us a foretaste and assurance that the Kingdom of God has broken out in our world.
Lord Jesus, may the light of your resurrection transfigure me this day, that those I meet today might see your glory reflected in me. Amen.
Luke 9:28-36 (NRSV)
28 Now about eight days after these sayings Jesus took with him Peter and John and James, and went up on the mountain to pray.
29 And while he was praying, the appearance of his face changed, and his clothes became dazzling white.
30 Suddenly they saw two men, Moses and Elijah, talking to him.
31 They appeared in glory and were speaking of his departure, which he was about to accomplish at Jerusalem.
32 Now Peter and his companions were weighed down with sleep; but since they had stayed awake, they saw his glory and the two men who stood with him.
33 Just as they were leaving him, Peter said to Jesus, "Master, it is good for us to be here; let us make three dwellings, one for you, one for Moses, and one for Elijah" --not knowing what he said.
34 While he was saying this, a cloud came and overshadowed them; and they were terrified as they entered the cloud.
35 Then from the cloud came a voice that said, "This is my Son, my Chosen; listen to him!"
36 When the voice had spoken, Jesus was found alone. And they kept silent and in those days told no one any of the things they had seen.