Ephesians 4:29

Corrupt. Gr. sapros, “rotten,” “putrid,” “bad.” In Matt. 7:17 sapros describes a corrupt tree, and in Matt. 13:48 inedible fish that were thrown away. Foul speech is the sign of a corrupt heart, “for out of the abundance of the heart the mouth speaketh” (Matt. 12:34). Profanity and obscene jests and songs, even the frivolous and insipid conversation, have no place in the Christian’s life; indeed, they are the hallmark of the unregenerate spirit.

Which is good. It is not enough that the Christian merely abstain from unseemly speech. His words are to accomplish a useful purpose. Jesus warned against the use of idle words (Matt. 12:36), words that accomplish no good purpose.

To the use of edifying. Literally, for the “upbuilding of the need.” Compare the translation, “edifying, as fits the occasion” (RSV). While speaking does not always have to be of a somber or even serious character, it should always edify or build up, making men better than they were before they heard the words. As in v. 28 the Christian’s work was to be for the benefit of others, so here his words also are to be for the good of his fellow men. Not only indecent speech but also that which is selfish, malicious, critical, or suggestive, corrupts. Here again the apostle seems to have in the back of his mind the central theme of his epistle — unity. That which does not edify tears down, and is therefore to be discarded. Compare 1 Thess. 5:11-14.

Grace. Gr. charis, here probably meaning “benefit” (cf. on Rom. 3:24).