Ambrose of Milan : Tell me, then, whoever you are who deny the divinity of the Holy Spirit. The Spirit could not be liable to sin, who rather forgives sin. Does an angel forgive? Does an archangel? Certainly not, but the Father alone, the Son alone and the Holy Spirit alone [can forgive sins]. Now one is obviously able to avoid that which he has power to forgive.But perhaps someone will say that the seraph said to Isaiah, "Behold, this has touched your lips and shall take away your iniquities and purge away your sins." Shall take away, he says, and shall purge, not I will take away, but that fire from the altar of God, that is, the grace of the Spirit. For what else can we piously understand to be on the altar of God but the grace of the Spirit? Certainly not the wood of the forests or the soot and coals. Or what is so in accordance with piety as to understand according to the mystery that it was revealed by the mouth of Isaiah that everyone should be cleansed by the passion of Christ, who as a coal according to the flesh burnt up our sins, as you read in Zechariah: "Is not this a brand snatched from the fire? Now Joshua was clothed in filthy garments." — On the Holy Spirit 1.10.112 Gregory the Dialogist : But Dionysius the Areopagite, that ancient and venerable Father, is said to declare that from the lesser hosts of angels some are sent forth to fulfill their ministry either visibly or invisibly, namely because angels or archangels come for human consolation. For those higher hosts never withdraw from the inner places, since those who are preeminent have no function of external ministry. This seems to be contradicted by what Isaiah says: "And one of the Seraphim flew to me, and in his hand was a coal which he had taken with tongs from the altar, and he touched my mouth." But in this statement of the prophet, he wants it understood that the spirits who are sent receive the name of those whose office they perform. For the angel who carries a coal from the altar to burn up the sins of speech is called a Seraphim, which means burning. — Forty Gospel Homilies, Homily 34 Origen of Alexandria : We read also in Isaiah that the prophet is purified with fire by "one of the seraphim which was sent to him, when he took with a pair of tongs one coal from those which were upon the altar; and he touched the lips of the prophet and said, Behold, I have taken away your iniquities." These appear to me to be mystical and to indicate that the coals are put on the members of each in proportion to his sins, if he is worthy to be purified. For since the prophet says here, "I have unclean lips; also I dwell in the midst of a people who have unclean lips." For this reason, "a coal taken up with a pair of tongs" by the seraphim cleanses his lips.… The cleansing of his lips indicates that Isaiah's sin continually would be found only in words, but he would not have sinned in any act or deed. Otherwise, he would have said since I have an unclean body or I have unclean eyes, if he had sinned in desiring what belongs to something other than his lips. He would have said I have unclean hands, if he had polluted these with unjust deeds. But now since possibly he was aware of his transgression in word alone, about which the Lord says, "Likewise, you will give an account for every useless word on the day of judgment"; because it is difficult even for the perfect to escape the fault of the word, the prophet was likewise in need only of a purification of his lips. — HOMILIES ON Leviticus 9:7.2 Peter Chrysologus : But let us at this time feel remorse with all the affection of our hearts. Let us admit that we are wretched in this misery of the flesh. Let us weep with holy groans because we, too, have unclean lips. Let us do all this to make that one of the seraphim bring down to us, by means of the tongs of the law of grace, a flaming sacrament of faith taken for us from the heavenly altar. Let us do this to make him touch the tip of our lips with such delicate touch as to take away our iniquities, purge away our sins and so enkindle our mouths to the full flame of complete praise that the burning will be one that results in salvation, not pain. Let us beg, too, that the heat of that coal may penetrate all the way to our hearts. Thus we may draw not only relish for our lips from the great sweetness of this mystery but also complete satisfaction for our senses and minds. — SERMON 57