Cassiodorus : By "mouth" [or lips] is meant the hidden region of the heart, from which God's praise is efficaciously sung. So he rightly proclaims after the forgiveness of his sin that his lips will be opened and that his mouth can announce the praise of the Lord. — EXPOSITION OF THE Psalms 5:17 Cassiodorus : We must especially follow the commandments, and signing our lips with the seal of the cross we must pray to the Lord that he may cleanse our mouths, which are disfigured with human foulness. — EXPOSITION OF THE Psalms 141:8 Desert Fathers : Mathois said, 'The nearer a man comes to God, the more he sees himself to be a sinner. Isaiah the prophet saw the Lord and knew himself to be wretched and unclean (Is. 6:5).' — The Desert Fathers, Sayings of the Early Christian Monks Gregory the Dialogist : Purity of heart and simplicity, Peter, is of great force with almighty God, who is in purity most singular, and of nature most simple. For those servants of his, which do retire themselves from worldly affairs, avoid idle words, labour not to lose their devotion, nor to defile their soul with talking, do especially obtain to be heard of him, to whom, after a certain manner, and as they may, they be like in purity and simplicity of heart. But we that live in the world, and speak oftentimes idle words, and that which is worse, sometime those that be hurtful: our words and prayers are so much the farther off from God, as they be near unto the world: for we are drawn too much down towards the earth, by continual talking of secular business: which thing the prophet Esaye did very well reprehend in himself, after he had beheld the King and Lord of armies, and was penitent, crying out: Woe be to me for being silent, because I am a man that have defiled lips: and he sheweth straight after the reason why his lips were defiled, when he saith: I dwell in the midst of a people that hath defiled lips. For sorry he was that his lips were defiled, yet concealeth not from whence he had them, when he saith, that he dwelt in the midst of a people that had defiled lips. For very hard it is that the tongues of secular men should not defile their souls, with whom they talk; for when we do sometime condescend to speak with them of certain things, by little and little we get such a custom, that we hear that spoken with pleasure which is not meet to be heard at all, so that afterward we are loath to give that over, to which at the first, to gratify others, we were brought against our wills. And by this means we fall from idle words to hurtful speeches, and from talk of small moment to words of great importance: and so it cometh to pass that our tongue is so much the less respected of God when we pray, by how much we are more defiled with foolish speech, because, as it is written: He that turneth away his ear that he hear not the law, his prayer shall be execrable. What marvel, then, is it, if, when we pray, God doth slowly hear us, when as we hear God's commandments, either slowly or not at all? — Dialogues, Book 3, Chapter 15 Jerome : According to the Hebrew, Isaiah cries out in anguish and says, "Woe is me because I have held my peace, because I am a man of unclean lips and I dwell in the midst of a people that has unclean lips, and I have seen with my eyes the Lord of hosts!" Because of his virtues, he deserved to enjoy the sight of God, and, because of his awareness of his sins, he confessed that his lips were unclean. Not because he had said anything that was contrary to the will of God, but because he had held his peace, deterred either by fear or modesty, and because he had not exercised the prerogative of a prophet, of condemning a sinful nation. When we, who flatter the rich and accept sinful persons, rebuke sinners, is it for the sake of base gain? Unless, perhaps, we speak with complete frankness to those whose wealth we stand in need of. We may act otherwise; we may refrain from every type of sin, but, if we keep silent about the truth, we are certainly committing a sin. — Against the Pelagians 2.24 Jerome : (Verse 5.) And I said: Woe to me because I have kept silent, for I am a man with unclean lips, and I dwell in the midst of a people with unclean lips, and I have seen the king, the Lord of hosts, with my own eyes. And after Abraham saw the Lord and heard His voice, he declared himself to be mere dust and ashes (Gen. 18). And Isaiah, according to the Septuagint, testifies that he was stricken, not for any other sins, but because he had unclean lips. Blessed is the conscience that has only sinned in speech, not by its own fault, but because of association with a people with unclean lips, with whom he was often compelled to speak. From this it is shown to be harmful to live with sinners: For he who touches pitch, will be defiled by it (Ecclesiasticus 13:1). But because we read in Hebrew: Woe is me, for I have kept silence, the Prophet laments, because he was not worthy to praise the Lord of Hosts with the Seraphim, whom we understand to be Angelic virtues. But he dared not praise the Lord, because he had unclean lips. And therefore he had unclean lips, because he associated with the sinful people. Certainly, it must be understood in this way: Because I remained silent and did not boldly rebuke the wicked king Ozias, therefore my lips are unclean, and I dare not sing praises to the Lord with the angels, lest it be said of me: Why do you declare my justices and take my covenant in your mouth? (Ps. 49:16) For there is no beautiful praise on the lips of a sinner. (Eccl. 15:9) However, we say this, not that we teach that Isaiah was such; but that he himself, out of humility and with only unclean lips, confesses himself worthy of God's praise. — Commentary on Isaiah Sahdona the Syrian : Let us, therefore, show awe when we sinners stand in the presence of this Majesty and speak. Even though we are so impure in our deeds he draws us close to the sight of himself in the Spirit; let us therefore repeat with trembling the words of the blessed prophet Isaiah: "Woe is me, for I am dazed: I am a man of unclean lips, yet my eyes have beheld the King, the Lord Almighty."He can be seen by us in the Spirit even now, if we wish—not that he is contained on the throne in any form external to his nature, just "filling the temple with the extremity of his train," as the prophet beheld. No, he is hidden in the loftiness of his hiddenness in the inaccessible light of his nature where he lives and reigns over all the extremities of the universe in the majesty of his dominion.… His creation is full of the splendor of his glory: "the seraphim" of fire "stand" there to honor him, the ranks of the many-eyed "cherubim" escort his majestic Being, the bands of spiritual powers dash around ministering to him, the throngs of angels fly hither and thither with their wings, and all the orders of spiritual beings serve his Being in awe, crying "holy" in trembling and love, "as they cover their faces" with their wings at the splendor of his great and fearful radiance, ceaselessly crying out to one another the threefold sanctification of his exalted glory, "saying, holy, holy, holy, Lord Almighty, with whose glories both heaven and earth are full." Let us therefore tremble at the magnitude of the sight of the ineffable one and at the sound that ceaselessly utters the praise of the hidden Being. And let us be filled with awe and trembling, falling on our faces in fear before him. Let us recognize our earthborn nature. Let us be aware of the base character of the dust we are made from. Let us join the prophet in saying, with feeling and with a penitent heart, "Woe is our state of confusion." Let us lay bare the foulness of our sins quite openly, accusing ourselves forcefully—just as it is said: "The just man condemns himself at the very beginning of his words." This is what we too should do at the commencement of our prayer, stating before God that we are not worthy to stand in his presence in our wretched state; and that, because our blind hearts have lost their sight through concentrating on what is below, dwelling in the darkness of the earth, we are unable to gaze on the great sight of him whose glory blinds the vision of the angels of light. Again, how are we able to speak with unclean lips about his great holiness? — BOOK OF PERFECTION 5-9