Even Angels Hide From God's Holiness

"Above him were seraphs, each with six wings: With two wings they covered their faces, with two they covered their feet, and with two they were flying." (Isaiah 6:2)

"The seraphim are not sinful humans burdened with impure hearts. Yet as angelic beings, they are still creatures, and even in their lofty status as consorts of the heavenly host it is necessary for them to shield their eyes from a direct gaze on the face of God. They are fearfully and wonderfully made, equipped by their Creator with a special pair of wings to cover their faces in His majestic presence.

"The seraphim have a second pair of wings. The second pair is used to cover their feet. This equipment is not intended as a sort of angelic shoe to protect the soles of their feet or to facilitate walking in the heavenly temple. The covering of the feet is for a different reason, a reason reminiscent of Moses' experience with the burning bush:

There the angel of the LORD appeared to him in flames of fire from within a bush. Moses saw that though the bush was on fire it did not burn up. So Moses thought, "I will go over and see this strange sight--why the bush does not burn up."

When the LORD saw that he had gone over to look, God called to him from within the bush, "Moses, Moses!"

And Moses said, "Here I am."

"Do not come any closer," God said. "Take off your sandals, for the place where you are standing is holy ground." (Exodous 3:2-5)

"God commanded Moses to take off his shoes. Moses was standing on holy ground. The ground was made holy by the presence of God. The act of removing the shoes was a symbol of Moses' recognition that he was of the earth--earthly. Human feet, sometimes called "feet of clay," symbolize our creatureliness. It is our feet that link us to the earth.

"The seraphim are not of the earth Their feet are not made of clay. As angels, they are spirit beings. Nevertheless they remain creatures, the imagery of Isaiah's vision suggests that they too must cover their feet, acknowledging their creatureliness in the exalted presence of God." 

R.C. Sproul, The Holiness of God, (Tyndale, 1998), p. 23-24.