Why Moses and Elijah?

'Tis good, Lord, to be here,
Thy beauty to behold,
where Moses and Elijah stand,
Thy messengers of old.

The collect for Transfiguration used to say "has confirmed the mysteries of the faith by the testimony of the fathers" but now it says "by the testimony of Moses and Elijah." So my mind stumbled over that while Pastor was saying the words during the prayer. But it got me to thinking during the readings and the sermon. WHY Moses and Elijah? Why were they the ones on the mountain?

And here's my suspicion. They were (if my memory is working right) the only ones who
1) saw God, and
2) had their lives threatened for being faithful prophets.

Abraham and Jacob and Joshua saw God.
All sorts of prophets were either killed by their people, or were in danger of being killed by their hearers: Jeremiah, David, Isaiah, etc.

But I can't think of anybody but Moses and Elijah who were there with God, talking to Him, not necessarily face-to-face, but physically present with Him, AND who were with God at that moment because their lives were in danger due to their preaching.