Exodus 33:20 (NKJV)
20 But He said, “You cannot see My face; for no man shall see Me, and live.”
Isaiah 6:1-2 (NKJV)
1 In the year that King Uzziah died, I saw the Lord sitting on a throne, high and lifted up, and the train of His robe filled the temple. 2 Above it stood seraphim; each one had six wings: with two he covered his face, with two he covered his feet, and with two he flew.
In Exodus God made it very clear that no man can look at the brightness of his glory & live,so could the Seraphim have covered their faces because of the glory of his presence