According to Protestantism, what is the significance of Jesus and the Mount of Transfiguration? Matthew, Mark and Luke all record the story of Jesus on the Mount of Transfiguration.  Matthew's version is provided below.

It seems that each writer simply records that the event occurred, but none of them seem to indicate why it was important.  Did it fulfill prophecy?  Was it just another authentication of Jesus' divinity?  Are Moses and Elijah somehow significant to be the ones speaking with Jesus?

According to Protestant understanding (and Catholic if it carries over), what is the significance or importance of Jesus on the Mount of Transfiguration?


  And after six days Jesus took with him Peter and James, and John his
  brother, and led them up a high mountain by themselves. 2 And he was
  transfigured before them, and his face shone like the sun, and his
  clothes became white as light. 3 And behold, there appeared to them
  Moses and Elijah, talking with him. 4 And Peter said to Jesus, “Lord,
  it is good that we are here. If you wish, I will make three tents
  here, one for you and one for Moses and one for Elijah.” 5 He was
  still speaking when, behold, a bright cloud overshadowed them, and a
  voice from the cloud said, “This is my beloved Son, with whom I am
  well pleased; listen to him.” 6 When the disciples heard this, they
  fell on their faces and were terrified. 7 But Jesus came and touched
  them, saying, “Rise, and have no fear.” 8 And when they lifted up
  their eyes, they saw no one but Jesus only.
  
  9 And as they were coming down the mountain, Jesus commanded them,
  “Tell no one the vision, until the Son of Man is raised from the
  dead.” 10 And the disciples asked him, “Then why do the scribes say
  that first Elijah must come?” 11 He answered, “Elijah does come, and
  he will restore all things. 12 But I tell you that Elijah has already
  come, and they did not recognize him, but did to him whatever they
  pleased. So also the Son of Man will certainly suffer at their hands.”
  13 Then the disciples understood that he was speaking to them of John
  the Baptist.  [Matthew 17:1–13 (ESV)]
John 5:39 You study the Scriptures diligently because you think that in them you have eternal life. These are the very Scriptures that testify about me...


A common refrain in sermons (and I've used this myself!) on the Transfiguration is that Jesus is being shown to be "the Word."

Historically, Jesus referred to the Scripture as "the Law and the Prophets," referencing a common idiom of the time.  Of these, 


Moses is clearly the "Lawgiver," in that he is identified with the Covenant most closely.
Elijah is the "Prophet," the first in a line and the prototype of many.


By appearing with "the Law" (Moses) and "the Prophets" (Elijah), Jesus is shown to be fufilling all of Scripture.