The Bible’s Answer
Yes, according to the Bible, swearing is a sin. In Paul’s letter to the Colossians, he wrote: “But now you must put them all away: anger, wrath, malice, slander, and obscene talk from your mouth” (Colossians 3:8, ESVUK). Obscene talk refers to any kind of word or phrase that is widely considered offensive, rude, or impolite in society. This, of course, would include swear words. Therefore, all people—especially Christians—should strive to refrain from swearing, both in public and private, and instead speak in a way that honours God.
Watch What You Say
The Lord Jesus Christ himself had a few words to say about speaking carelessly. Shortly after the Pharisees had falsely accused Jesus of casting out demons by Beelzebul (Satan), rather than the Holy Spirit, Jesus said:
Either make the tree good and its fruit good, or make the tree bad and its fruit bad, for the tree is known by its fruit. You brood of vipers! How can you speak good, when you are evil? For out of the abundance of the heart the mouth speaks. The good person out of his good treasure brings forth good, and the evil person out of his evil treasure brings forth evil. I tell you, on the day of judgement people will give account for every careless word they speak, for by your words you will be justified, and by your words you will be condemned. (Matthew 12:33–37)
Two significant things should be noted from this passage. 1. On judgement day, God will not only judge us according to our deeds, but our words, too. This means that we can sin in what we say. 2. People with a pure heart will speak good things, but people with impure hearts will speak evil things.
Ultimately, the only one who can purify and change our hearts is the Holy Spirit, who dwells in Christians and daily conforms them to Christ’s image (2 Corinthians 3:18; Romans 8:29). However, even Christians, who have been born again (John 3:3–5), can succumb to temptations of their sinful flesh, and not walk in the Spirit for a time (Galatians 5:16–17). Therefore, we, too, need to watch what comes out of our mouths—even if no one but God can hear us (Psalm 94:9–11)—and live in a manner worthy of Jesus Christ, who lives in Christians (Ephesians 3:17).
Speak Purely to Build Others Up
God encourages us to build others up in our speech and actions, rather than tear them down. The Apostle Paul wrote: “Let no corrupting talk come out of your mouths, but only such as is good for building up, as fits the occasion, that it may give grace to those who hear” (Ephesians 4:29). Corrupting talk consists of things like swearing, gossip, and crude jokes (Ephesians 5:4), and clearly, such things do not “give grace” to those who hear. Some key things to ask yourself, when you feel like using a foul word, would be: would Jesus be pleased if I spoke in such a way? Will this corrupting talk build me or others up, or will it bring disgrace upon myself and make others feel uncomfortable? Would I speak this way in front of a child? If in doubt, it is best to refrain.
Notice, also, what Paul said when teaching about what true love is: “Love is patient and kind; love does not envy or boast; it is not arrogant or rude. It does not insist on its own way; it is not irritable or resentful; it does not rejoice at wrongdoing, but rejoices with the truth. Love bears all things, believes all things, hopes all things, endures all things” (1 Corinthians 13:4–7). Notice how he said that love is not rude and does not rejoice at wrongdoing. Therefore, how can swearing, which is rude and sinful, be a loving thing to do? All Christians are under this command: “Let all that you do be done in love” (1 Corinthians 16:14). It is impossible to walk in the spirit of love and swear at the same time.
The Bible speaks against “obscene talk”, uttering “careless words”, and “corrupting talk”. The Bible teaches that true love is not rude, and commands Christians to do everything in love. Furthermore, we are to “give grace” to those to whom we are speaking, by doing so in a way that is honourable, kind, and decent. Because swearing goes against all of the above Bible teachings, we can safely say that it is indeed a sin, and therefore, something that we should all refrain from doing. If you have ever sworn and are genuinely sorry for it, then confess this sin to God (1 John 1:9), and trust in Jesus as your God and Saviour (Titus 2:13–14), and God will forgive you (Romans 8:1; Ephesians 2:8–9).