Jamieson, Fausset and Brown on Ephesians 4:29

29. corrupt--literally, "insipid," without "the salt of grace" (Col 4:6), so worthless and then becoming corrupt: included in "foolish talking" (Ep 5:4). Its opposite is "that which is good to edifying."

communication--language.

that which, &c.--Greek, "whatever is good."

use of edifying--literally, "for edifying of the need," that is, for edifying where it is needed. Seasonably edifying; according as the occasion and present needs of the hearers require, now censure, at another time consolation. Even words good in themselves must be introduced seasonably lest by our fault they prove injurious instead of useful. Trench explains, Not vague generalities, which would suit a thousand other cases equally well, and probably equally ill: our words should be as nails fastened in a sure place, words suiting the present time and the present person, being "for the edifying of the occasion" (Col 4:6).

minister--Greek, "give." The word spoken "gives grace to the hearers" when God uses it as His instrument for that purpose.