Think of what they saw and heard on the mountain, during the transfiguration. How grateful should we be that Our Lord reveals Himself to us! He doesn't let us "stay on the mountaintop" - it won't always be, nay, rarely will an experience of God be what keeps us faithful - but He gives us Himself in His word every day.
Think of Him today, on His day. Think of where He has been - to the mountains, to the depths, to the cross - and that He always comes back to us.
Sufjan Stevens reminds me of Him, because that's what he's aiming to do. Stevens's "The Transfiguration" is evocative of that event, down to the sounds the clouds might make when opening up for God's voice to come through. At least, that's what I hear in the song.