Above it stood the seraphim: each one had six wings; with two he covered his face, and with two he covered his feet, and with two he did fly.
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Eusebius of Caesarea
Some think there are two seraphim, but I, based on the idea expounded by the sacred Scripture, which says, “the seraphim stood round about him,” think there are many, and they are bodyguards, as it were, like a crown from all sides, surrounding his throne with light and enlivened by him. - "Commentary on Isaiah 6.2"
The two Seraphims "burning. "They are supposed to constitute the highest order of angels, Numbers xxi. 6.
His. God's or their own face. Hebrew and Septuagint are ambiguous. Out of respect, (Calmet) they looked not at the divine majesty. (Menochius)
Let us bring our discourse back to our earlier proposition and let us show that God, even by the accommodation of condescension, cannot be seen by the powers above. Tell me this. Why do the seraphim stretch forth their wings? There is no other reason than the statement made by the apostle: “Who dwells in unapproachable light.” And these heavenly virtues, who are showing this by their very actions, are not the only ones. There are powers higher than the seraphim, namely, the cherubim. The seraphim stood near; the cherubim are the throne of God. They are not called this because God has need of a throne but so that you may learn how great is the dignity of these very powers. - "Against the Anomoeans 3.24"