"When Christ was transfigured on the mountain, Moses and Elias appeared conversing with Him. Why were these two present, out of all the righteous of the Old Testament? The service texts explain this. There are two equally valid answers. One has to do with the respective ministries of the two saints, and the other with a very important difference between them." - Michael McKean

Curious points: The disciples recognized who those two men were without being told. Of course, every matter had to have two witnesses... and the symbolism of the Trinity is here. - Gus