Thomas Aquinas, on Eph 4:29

“Let no evil speech proceed from your mouth; but that which is good, to the edification of faith, that it may administer grace to the hearers.”

“When he states Let no evil speech proceed from your mouth he begins to discuss what the old man does in relation to other men. He makes two points: First, he prohibits the old and encourages the new. Secondly, he provides an example for imitation at the beginning of Chapter Five (5:1). A person may be wrongly disposed toward his neighbor in two ways. In one way, he may hurt him through evil words; in another, he may harm him through bad example. First he forbids the former, secondly the latter (4:30). The first of these also has two sections: First, he bans the old. Secondly, he urges them toward the new (4:29b). A word from the mouth exteriorizes or expresses whatever is on the mind since spoken words are signs of what occurs in the soul. A good word is one which indicates good interior dispositions, while an evil word externalizes evil dispositions. Man should possess a threefold inner relationship; namely, to himself, that all his powers are subject to reason; to God, so that his reason submits to him; and to his fellow man when he loves him as himself. Hence a word is evil when it shows that a man is not properly related within himself. This is the false word by which he means one thing and says another; futile and vain talk also belong to this category. Again, there are wicked words which indicate that a man is not related properly to God, such as perjury, blasphemy and the like. Finally, there is also evil talk which is against one's neighbor, such as injurious, deceitful, and fraudulent words. Therefore does he say Let no evil speech proceed from your mouth. "No" is equivalent to "none." "Keep yourselves therefore from murmuring which profiteth nothing, and refrain your tongue from detraction: for an obscure speech shall not go for nought" (Wis. 1:11). For God will certainly not forget any thought, "and no word can hide itself from him" as Ecclesiasticus 42 (20) remarks. "But now put away also any anger, indignation, malice, blasphemy, or filthy speech out of your mouth" (Col. 3:8). With "that which is good" he encourages them on toward newness because a good word, spoken at the right time and place, is blessed. "A word in due time is best" (Prov. 15:23). "If any man speak, let him speak as the words of God" (1 Pet. 4:11). And what for? He adds to the edification of faith in order, that is, for faith to be strengthened in the hearts of the weak: "Let all things be done to edification" (1 Cor. 14:26). If it may administer grace to the hearers such a word is proven good and it is profitable. For frequently a man repents and is disposed for grace from hearing a good sermon and through the power it conveys. "While Peter was yet speaking these words, the Holy Spirit fell on all them that heard the word" (Ac. 10:44). Our Lord spoke in this fashion; Luke 4 (22) recounts: "They wondered at the words of grace that proceeded from his mouth." "The words of the mouth of a wise man are grace" (Eccl. 10:12).”

Imported from an open dataset — not yet checked against the printed edition.