The verb “come out” or “proceed” (ekporeuestho) is a present-imperative. Paul does not offer a suggestion to heed or wise counsel to consider. He is issuing a command to be obeyed . . . always. No unwholesome, corrupting, rotten word (logos) should ever breach the larynx. By implication this includes unwholesome conversations and dialogue (so KJV, ESV, NIV).
How are we to tell what may be unwholesome or corrupt? What does it taste like? The word translated “unwholesome” (sapros) is used seven other times in the NT. It described the type of tree that produced bad fruit (Mt 7.17, 18; 12.33; Lk 6.43). It also described the type of fish that angels will throw away in the eschatological assize (Mt 13.48). The unwholesome word is any word unwelcome in the kingdom of God.
God will one day light the pilot light for heaven’s proverbial furnace. He will throw every word, thought and deed into it to test the quality of each man’s work (1 Cor 3.13). Whatever was worthy of the kingdom will come out shining like gold (v14). Whatever wasn’t will we cleaned out from the ash bin (v15). My sarcasm will be swept out with all the bad trees and junk fish. What will be left of my words and conversations?
It pains me to hear Jesus’ words to the Pharisees: “For the mouth speaks out of that which fills the heart” (Mt 12.34). This amazingly comes on the heels of v33, which speaks to the bad (sapros) tree and its evil fruit! The bad fruit-bearing tree equals the evil word-saying heart. My journey out of sarcasm is not so much a change in vocabulary, but a renovation of the heart. It’s a journey out of hate into love. Therefore, how much will be left of my heart after the furnace cools? Jesus, have mercy on me.
“I just can’t help it, it’s who I am” is no longer a viable excuse. If I have heard Jesus and and been taught in him (Eph 4.21) then I am to be renewed in the spirit of my mind (v23). We are commanded to be renewed, to put ourselves always in the way of the Spirit, to shed the old self and put on the new (v24). Therefore, I am commanded and able in Christ to keep any unwholesome word from escaping my lips. As with all aspects of sanctification, God commands nothing that he does not give us his strength and ability to obey. We remember Brother Augustine: “Give me the grace to do as you command, and command me to do what you will!” (Confessions, X.29)