A matter this more terrible and startling, as he also says in the Epistle to the Thessalonians; for there too he uses an expression of this sort. “He that rejects, rejects not man, but God.” So also here. If you utter a reproachful word, if you strike your brother, you are not striking him, you are “grieving the Holy Spirit.” And then is added further the benefit bestowed, in order to heighten the rebuke.
“And grieve not the Holy Spirit,” says He, “in whom you were sealed unto the day of redemption.”
He it is who marks us as a royal flock; He, who separates us from all former things; He, who suffers us not to lie among them that are exposed to the wrath of God—and do you grieve Him? Look how startling are his words there; “For he that rejects,” says he, “rejects not man, but God:” and how cutting they are here, “Grieve not the Holy Spirit,” says he, “in whom you were sealed.”
Moral. Let this seal then abide upon your mouth, and never destroy the impression. A spiritual mouth never utters a thing of the kind. Say not, “It is nothing, if I do utter an unseemly word, if I do insult such an one.” For this very reason is it a great evil, because it seems to be nothing. For things which seem to be nothing are thus easily thought lightly of; and those which are thought lightly of go on increasing; and those which go on increasing become incurable.
You have a spiritual mouth. Think what words you uttered immediately upon being born, — what words are worthy of your mouth. You call God, “Father,” and do you straightway revile your brother? Think, whence is it you call God, “Father”? Is it from nature? No, you could never say so. Is it from your goodness? No, nor is it thus. But whence then is it? It is from pure lovingkindness, from tenderness, from His great mercy. Whenever then you call God, “Father,” consider not only this, that by reviling you are committing things unworthy of that, your high birth, but also that it is of lovingkindness that you have that high birth. Disgrace it not then, after receiving it from pure lovingkindness, by showing cruelty towards your brethren. Do you call God “Father,” and yet revile? No, these are not the works of the Son of God. These are very far from Him. The work of the Son of God was to forgive His enemies, to pray for them that crucified Him, to shed His blood for them that hated Him. These are works worthy of the Son of God, to make His enemies—the ungrateful, the dishonest, the reckless, the treacherous—to make these brethren and heirs: not to treat them that have become brethren with ignominy like slaves.
Think what words your mouth uttered—of what table these words are worthy. Think what your mouth touches, what it tastes, of what manner of food it partakes! Do you deem yourself to be doing nothing grievous in railing at your brother? How then do you call him brother? And yet if he be not a brother, how do you say, “Our Father”? For the word “Our” is indicative of many persons. Think with whom you stand at the time of the mysteries! With the Cherubim, with the Seraphim! The Seraphim revile not: no, their mouth fulfills this one only duty, to sing the Hymn of praise, to glorify God. And how then shall you be able to say with them, “Holy, Holy, Holy,” if you use your mouth for reviling? Tell me, I pray. Suppose there were a royal vessel, and that always full of royal dainties, and set apart for that purpose, and then that any one of the servants were to take and use it for holding dung. Would he ever venture again, after it had been filled with dung, to store it away with those other vessels, set apart for those other uses? Surely not. Now railing is like this, reviling is like this. “Our Father!” But what? Is this all? Hear also the words, which follow, “which art in Heaven.” The moment you say, “Our Father, which art in Heaven,” the word raises you up, it gives wings to your mind, it points out to you that you have a Father in Heaven. Do then nothing, speak nothing of things upon earth. He has set you among that host above, He has numbered you with that heavenly choir. Why do you drag yourself down? You are standing beside the royal throne, and you revile. Are you not afraid lest the king should deem it an outrage? Why, if a servant, even with us, beats his fellow-servant or assaults him, even though he do it justly, yet we at once rebuke him, and deem the act an outrage; and yet do you, who art standing with the Cherubim beside the king's throne, revile your brother? Do you see not these holy vessels? Are they not used continually for only one purpose? Does any one ever venture to use them for any other? Yet are you holier than these vessels, yea, far holier. Why then defile, why contaminate yourself? Standest thou in Heaven, and do you revile? Have you your citizenship with Angels, and do you revile? Are you counted worthy the Lord's kiss, and do you revile? Hath God graced your mouth with so many and great things, with hymns angelic, with food, not angelic, no, but more than angelic, with His own kiss, with His own embrace, and do you revile? Oh, no, I implore you. Vast are the evils of which this is the source; far be it from a Christian soul. Do I not convince you as I am speaking, do I not shame you? Then does it now become my duty to alarm you. For hear what Christ says: “Whosoever shall say to his brother, You fool, shall be in danger of the hell of fire.” Now if that which is lightest of all leads to hell, of what shall not he be worthy, who utters presumptuous words? Let us discipline our mouth to silence. Great is the advantage from this, great the mischief from ill language. We must not spend our riches here. Let us put door and bolt upon them. Let us devour ourselves alive if ever a vexatious word slip out of our mouth. Let us entreat God, let us entreat him whom we have reviled. Let us not think it beneath us to do so. It is ourselves we have wounded, not him. Let us apply the remedy, prayer, and reconciliation with him whom we have reviled. If in our words we are to take such forethought, much more let us impose laws upon ourselves in our deeds. Yea, and if we have friends, whoever they may be, and they should speak evil to any man or revile him, demand of them and exact satisfaction. Let us by all means learn that such conduct is even sin; for if we learn this, we shall soon depart from it.
Now the God of peace keep both your mind and your tongue, and fence you with a sure fence, even His fear, through Jesus Christ our Lord, with whom to the Father, together with the Holy Spirit, be glory forever. Amen.
Source: Homilies on Ephesians (New Advent)