An extremely touching song - I love the song, the picture Isaiah paints in your mind.
And some thoughts on this song/ picture in the Bible.
A few other verses in the Bible like this is Exodus 33:7-23 (http://www.blueletterbible.org/Bible.cfm?b=Exd&c=33&v=7&t=NKJV#7 - NKJV)
As Yhwh stated "You cannot see My face; for no man shall see Me, and live."
If you remember within the tabernacle is the "Holy of Holy's" where the Ark of the Covenant rested. Carved into the Ark of the Covenant was the Mercy Seat, where Yhwh rested. On either side of the Mercy seat stood two Cherubim who. The cherubim "shall stretch out their wings above, covering the mercy seat with their wings, and they shall face one another; the faces of the cherubim shall be twoards the mercy seat." (Exodus 25:20)
This followes Isaiah 6 "with two (wings) he covered his face, with two he covered his feet, and with two he flew." (http://www.blueletterbible.org/Bible.cfm?b=Isa&c=6&v=1&t=NKJV#top - Isaiah 6 NKJV)
Isaiah is referring to Seraphim (plural), not Cherubim (also plural). However, I would like to make the observation that God tells Moses "now human can see my face" otherwise "they would die."
Exodus also states that Moses "The Lord spoke to Moses face to face" (Ex. 33:11). My hypothosis is that Moses did not die because the Cherubim on either side of the Mercy seat - facing the Mercy seat - wings extended - his the place where the Lord's Face was at. In a sense, a vail. A vail of a very holy, pure, perfect kind - created by the wings of Cherubim (and ultimately God himself since he created even these holy beings).
Just a passing thought based on todays Bible reading from Exodus 33 :-)
(Picture taken from http://images.google.com/imgres?imgurl=http://freegroups.net/ministry_files/mirrors/ichthys.com/tabernacle-temple.gif&imgrefurl=http://freegroups.net/ministry_files/mirrors/ichthys.com/Tribulation_Part_2B.htm&usg=__kMaC5dse3wBRqc9t0a3cVKZ-gBI=&h=443&w=511&sz=9&hl=en&start=13&sig2=AEg2zD6igjVPPeqnMVDG3g&um=1&tbnid=BRWnLEele6OfPM:&tbnh=114&tbnw=131&ei=OyEmSb_yGp3aNL31qDg&prev=/images%3Fq%3DPicture,%2Btabernacle%26um%3D1%26hl%3Den%26sa%3DX)