How do you eliminate foul language? A high school chose to institute a “no foul language” promise. The students took an oath, saying: "I do solemnly promise not to use profanities of any kind within the walls and properties of [our school].” This was a noble effort, but according to Jesus, no external rule or pledge can ever cover the odor of foul speech.

Removing the stench of the words that come from our mouths begins with renewing our hearts. Just as people recognize the kind of tree by the fruit it bears (Luke 6:43–44), Jesus said that our speech is a convincing indicator of whether our hearts are in tune with Him and His ways or not. Fruit stands for a person’s speech, “for the mouth speaks what the heart is full of” (v. 45). Christ was pointing out that if we really want to change what’s coming out of our mouths, we first have to focus on changing our hearts as He helps us.

External promises are useless to curb the foul language that comes forth from an untransformed heart. We can only eliminate foul speech by first believing in Jesus (1 Corinthians 12:3) and then inviting the Holy Spirit to fill us (Ephesians 5:18). He works within us to inspire and help us to continually offer thanks to God (v. 20) and to speak encouraging and edifying words to others (Ephesians 4:15, 29; Colossians 4:6).