Why Moses and Elijah in the Transfiguration
Truly, I say to you, there are some standing here who will not taste death until they see the Son of Man coming in his kingdom. (Matthew 16:28)
...especially when we know the apostles are no longer on our side of eternity, and the new kingdom has not arrived yet. Apparently I didn't try hard enough because this morning it just clicked and I got it. Just keep reading into chapter 17 and you get your answer, the Transfiguration.
This event (one of my favorites in scripture) is one of those unique times in the New Testament text when Jesus did something so extraordinary that He had to tell those with Him not to say anything until the time was appropriate. Peter seemed to sense it's importance, but why Moses and Elijah? Some commentaries suggest that the transfiguration was a preview to Jesus' kingdom to come. As described, Jesus' kingdom to come will have three different "people forms" present, and they are all laid out for us right here in Matthew 17, and key to understanding the kingdom to come is Moses and Elijah.
First, in the new kingdom, there are those in their present physical body, represented by the inner circle of disciples who were present at the transfiguration. Next, those people who have died or will die, represented at the transfiguration by Moses, and third, those saved individuals who will be called up to heaven alive and will not experience death (1 Thes. 4:17), represented by Elijah.
At that time Jesus will also be in His full glory, just as He was during the transfiguration... and seeing these things, the disciples were able to see the coming kingdom of Heaven before they died as described Matthew 16:28.
To me, these combined set of verses gives us the greatest hope for the promises of life after death. Jesus first revealed it to his inner circle of disciples and after His resurrection the disciples revealed this to all of us. This is overly simplified, but sometimes God's word is revealed to us a little at a time, and sometimes it's given to you in that ah ha moment. That's why it's the "living" word and not just marks on a page.