And one cried unto another, and said, Holy, holy, holy, is the LORD of hosts: the whole earth is full of his glory.
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Ambrose of Milan
AD 397
Cherubim and seraphim with unwearied voices praise him and say, “Holy, holy, holy is the Lord God of hosts.” They say it not once, lest you should believe that there is but one; not twice, lest you should exclude the Spirit; they say not holies [in the plural], lest you should imagine that there is plurality, but they repeat three times and say the same word, that even in a hymn you may understand the distinction of persons in the Trinity and the oneness of the Godhead, and while they say this they proclaim God. - "On the Holy Spirit 3.16.110"
What are we going to do there? Tell me. Sleep? Yes, here people who have nothing to do just sleep. But there is no sleep there, because there is no weariness. So we aren’t going to perform works of necessity, aren’t going to sleep—what are we going to do? None of us must be afraid of boredom; none of us must imagine it’s going to be so boring there. Do you find it boring now to be well? You can get tired of anything and everything in this age; can you get tired of being well? If you don’t get tired of good health, will you get tired of immortality? So what activity are we going to engage in? “Amen” and “Alleluia.” Here, you see, we do one thing and another, there one thing, I don’t say day and night but day without end; what the powers of heaven, the seraphim, say now without ever getting bored: “Holy, holy, holy, Lord God of hosts.” - "Sermon 211a2"
Isaiah, too, includes one Holy Spirit in the glory of the Trinity when he says, “I saw the Lord seated on a high throne; seraphim were stationed above and cried one to the other, “Holy, holy, holy is the Lord of hosts!” And in a following passage he says, “I heard the voice of the Lord saying, ‘Go and say to this people: Listen carefully, but you shall not understand! Look intently, but you shall see nothing!’ ” - "Sermon 212.3"
In announcing that the whole earth is full of his glory, the seraphim are predicting the mystery of the economy that will be brought to pass through Christ. Prior to the Word’s becoming flesh the world was ruled by the devil, the evil one, the serpent, the apostate. The creature, rather than the Creator, was worshiped. But when the only-begotten Word of God became human, the entire earth was filled with his glory. - "Commentary on Isaiah 1.4"
The mouths of the seraphim are filled with blessings. They offer a doxology in turn, not in my opinion because they are tired but because they show respect to one another, both receiving and giving the doxology. They say “holy” three times and then conclude with “Lord of hosts.” This demonstrates that the Holy Trinity exists in one divine essence. All hold and confess that the Father exists, along with the Son and the Spirit. Nothing divides those who are named nor separates them into different natures. Just the opposite is true. We recognize one Godhead in three persons. - "Commentary on Isaiah 1.4"
We make mention also of the seraphim, whom Isaiah in the Holy Spirit saw standing around the throne of God, and with two of their wings veiling their face, and with two their feet, while with two they flew, crying, “Holy, holy, holy is the Lord of hosts.” For the reason of our reciting this confession of God, delivered down to us from the seraphim, is this, that so we may be partakers with the hosts of the world above in their hymn of praise. - "Catechetical Lectures 23.6"
The prophet Isaiah did not keep silent about this Trinity of persons and unity of nature revealed to him, when he says he saw the seraphim crying out, “Holy, holy, holy, Lord God of hosts.” Therefore, where the triple “holy” is repeated, there is the Trinity of persons; where “God Lord of hosts” is said but once, we recognize the unity of the divine nature. Therefore, in that Holy Trinity—and I keep on saying it so that it may be fixed in your heart the more firmly—the Father is one, who alone by his nature has generated the one Son from himself; and the Son is one, who alone has been born from the nature of the one Father; and the Holy Spirit is one, who alone proceeds from the essence of the Father and the Son. All of this is not possible for one person, that is, to generate oneself and to be born of oneself and to proceed from oneself. Therefore, because generating is different from being born and proceeding is something different again from generating and being born, it is obvious ...
Because they cry out one to another or, according to the Hebrew, this one to that one, that is, mutually, they are exhorting each other to the praise of the Lord. And they say “Holy, holy, holy, Lord of hosts,” that the mystery of the Trinity in one divine nature might be displayed. They also declare that no longer is it true only of the temple of the Jews, as before, but the whole earth is filled with the glory of him who deigned to assume a human body for our salvation and descend to earth. Moreover, when Moses had prayed to ask the Lord to spare this sinful people who had worshiped a calf, the Lord responded, “I will forgive them. Yet I live, and my name lives, for all the earth will be filled with my glory.” And the seventy-first psalm sings, “All the earth will be filled with his glory.” For this reason also did angels call to the shepherds, saying, “Glory to God in the highest and peace on earth to men of good will.” It is impious, therefore, to understand the two seraphim to be ...
What, then, do you think? Do you think that the angels in heaven talk over and ask each other questions about the divine essence? By no means! What are the angels doing? They give glory to God, they adore him, they chant without ceasing their triumphal and mystical hymns with a deep feeling of religious awe. Some sing, “Glory to God in the highest”; the seraphim chant, “Holy, holy, holy,” and they turn away their eyes because they cannot endure God’s presence as he comes down to adapt himself to them in condescension. - "Against the Anomoeans 1.35"
Do you desire to learn how the powers above pronounce that name; with what awe, with what terror, with what wonder? “I saw the Lord,” says the prophet, “sitting upon a throne, high, and lifted up; around him stood the seraphim; and one cried to another and said, “Holy, holy, holy, Lord God of hosts; the whole earth is full of his glory!” Do you perceive with what dread, with what awe, they pronounce that name while glorifying and praising him? But you, in your prayers and supplications, call upon him with much listlessness; when it would become you to be full of awe and to be watchful and sober! - "Homily Concerning the Statues 7.9"
The scriptural declaration “they cried out to one another” means, I think, that they ungrudgingly impart to each other the conceptions resulting from their looking on God. And we should piously remember that in Hebrew the Scripture gives the designation of seraphim to the holiest of beings in order to convey that these are fiery hot and bubbling over forever because of the divine life which does not cease to bestir them. - "Ecclesiastical Hierarchy 4.3.9"
