"Transfiguration" is an odd word, so I consulted my dictionary. It said that it means "a marked change in form or appearance; a metamorphosis; a change that glorifies or exults". It also told me that the feast of the Transfiguration is on August the 6th (19th in the Eastern Orthodox Church), but then it was an Internet dictionary I was consulting and just goes to prove that not everything you read there is useful: of use though, is that definition: "a marked change in form or appearance", which we'll come back to.
This sermon will first look at the context, then Peter, then Jesus, then our faith and finally arrive at what I see as the challenge of this passage for us today.
In the walking on the water story, Peter takes an even more common male approach: he offers to do something. However, Jesus takes him up on it and he has to step out of the boat.
So, back on the mountain, Peter didn't sit there and think "now then - how ought I to respond to this strange and somewhat unsettling event that is taking place before me?", meditating upon possible approaches and coming to a considered opinion of the most appropriate response to the Transfiguration (pausing briefly to look the word up on the Internet) but instead responded by offering to do something - he responded as a man of action and activity, he responded as himself.
I see a pattern in this that seems to hold true: we believe and then see miracles, not the other way round. We ask in prayer, believing we will be answered, and see the answers - not the other way round (something to bear in mind as we begin the 40 days course). Faith comes first, then the evidence, thereby increasing the faith we started out with. Those who say they are waiting for "proof" won't see it - it's given to those that don't really need it. Proof, if you like, is a reward for faith, not a reason for it.
So we see Jesus, suddenly transfigured in all his godly splendour and, just in case we don't yet understand what's going on, there's the voice from heaven to make it clear.
The voice though, not only confirms that Jesus is God's Son, but issues a command: "Listen to Him" (v.5). This is interesting because that was precisely what the disciples hadn't been doing recently - after Peter's confession of Jesus as the messiah at Caesarea Philippi, Jesus had begun to teach them about His path to glory - the necessity for His death on the cross and, through it, our redemption and salvation. Yet Peter even took Jesus to one side and told Him off. The voice's command to "Listen to Him" gains an additional significance in this context - what Jesus was telling the disciples about His mission wasn't just an idea - it was an essential part of God's plan to redeem His people.
Equally important is that Jesus was transfigured, not transformed. He was not transformed into God's Son, but already was God's Son: the transfiguration is a revelation, not a transformation. Jesus didn't attain divinity on the mountain: He already had it. Again, without this, God's plan for our redemption and salvation wouldn't work.
During the Transfiguration Jesus meets with Moses and Elijah. Why them? Why not other Old Testament heroes like David or Abraham, Solomon or Ruth? The reason, most commentators agree, is symbolic: Moses represents the Law and Elijah the Prophets. Both were fulfilled by Jesus. Luke even tells us what they talked about: the fulfilment of Jesus' mission to redeem mankind through Jesus' death on the cross (Lk 9 v 31). That alone is interesting when you consider that Moses lived to a very old age and Elijah was spared death and passed straight into Heaven. Both are fates that you would think befitted anyone good or important - let alone God's only Son. Yet such is the love of God for us, that Jesus wasn't allowed either of them: He died in a horrible fashion - because God loves us.
Finally, as Matthew tells us, when Moses & Elijah have gone, the disciples are terrified: yet Jesus comes and touches them, saying "Don't be afraid". When they are afraid of his divinity, His humanity reaches them. God's physical presence on Earth touches them and breaks through their fear: God incarnate come to be with them. Emmanuel - God is with us, as we sing so often at Christmas.
The transfiguration, then, is a point at which Jesus' nature and God's plan for our salvation are clearly revealed: Jesus is divine. Jesus fulfils the Law and the Prophets. Jesus will die in our place, to bring us back to God.