The quick answer is, yes, it is a sin to cuss or swear or curse. Ephesians 4:29 says, "Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen." That seems pretty clear! Also, 1 Peter 3:10 adds, "For whoever would love life and see good days must keep his tongue from evil and his lips from deceitful speech." Not clear enough yet? James 3:9-12 says, "With the tongue we praise our Lord and Father, and with it we curse human beings, who have been made in God’s likeness. Out of the same mouth come praise and cursing. My brothers and sisters, this should not be. Can both fresh water and salt water flow from the same spring? My brothers and sisters, can a fig tree bear olives, or a grapevine bear figs? Neither can a salt spring produce fresh water."
I love this example in James, where he's saying that Christians should not be known for a tendency to swear. His analogy of salt water and fresh water coming from the same spring (which is completely unnatural) shows how unnatural it would be for a Christian to praise God one minute and cuss someone out the next. If that seems really weird, it’s supposed to. It is not natural for a true believer to curse—at least, it shouldn't be.
We all get angry and want to say hurtful things sometimes, but Jesus says that what comes out of our mouths is a reflection of what is in our hearts. Evil in one’s heart will eventually be expressed in curses or swearing. On the flipside, if our hearts are filled with the love of God, others, and His goodness, that is what we will express with our words. “The good man brings good things out of the good stored up in his heart, and the evil man brings evil things out of the evil stored up in his heart. For out of the overflow of his heart his mouth speaks” (Luke 6:45). What do you want flowing out of your mouth?
So you may still be wondering: Why is it a sin to cuss/swear/curse? Sin reveals itself through our thoughts and actions; it's a condition of the “inner man” (Romans 7:22). When we use cuss words, we are expressing that nasty sin in our hearts, which we need to confess and ask God’s forgiveness for. Thankfully, our awesome God is “faithful and just and will forgive us our sins and purify us from all unrighteousness” (1 John 1:9). When we are ready to receive God’s forgiveness, we'll get a new attitude and nature from God (2 Corinthians 5:17). We'll see our speech change to reflect God's holiness.
Here’s the deal. Everything you say can be used to build someone up or break them down. Insulting others, in a way, insults God because He made every person you will ever encounter (Proverbs 17:5). It’s like when you were little and spent an hour on that Play-Doh dog you were so proud of. Then your little brother comes in and says, “That’s the dumbest Play-Doh dog I’ve ever seen!” You would be insulted right? That’s kind of the same concept when you insult God’s creation, including people—or anything else for that matter. (No, I am not comparing you to Play-Doh. You are much more important than that. ☺)
Will you use your words to build up others and glorify God? Or use them to cut people down and insult God and His creations? If you’re struggling with keeping ahold of your tongue, ask God to help you and start filling your heart with His love so that your words will express it.
We all get angry and want to say hurtful things sometimes, but Jesus says that what comes out of our mouths is a reflection of what's in our hearts. Evil in one’s heart will eventually be expressed in curses or swearing (Ephesians 4:29). But if our hearts are filled with the love of God, others, and His goodness, that is what we will express with our words (Luke 6:45; Romans 7:22). Everything you say can be used to build someone up or break them down. Which will you choose to do?
Jenny is a teenager who likes to sing, play instruments, and play volleyball. God has blessed her incredibly with a wonderful church, family, and friends. He taught her so much on a recent missions trip to Mexico, and she can't wait to go again. She's joyful and likes to have fun.