Is it a sin to say bad words?
Is swearing / cussing / cursing a sin?
Christians are clearly taught, "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). This would certainly include cussing or foul language.
James also directly addressed this issue of the power of the tongue: "With it we bless our Lord and Father, and with it we curse people who are made in the likeness of God. From the same mouth come blessing and cursing. My brothers, these things ought not to be so" (James 3:9-10). A believer in Christ is to use his or her words to bless others, not to curse.
James also addresses the topic of swearing: "But above all, my brothers, do not swear, either by heaven or by earth or by any other oath, but let your 'yes' be yes and your 'no' be no, so that you may not fall under condemnation" (James 5:12). This verse speaks specifically not of swear words, but rather swearing in the context of making promises, such as, "I swear on my mother's grave I will be there on time." A believer in Christ does not need to make such statements. Instead, believers are to be known for their integrity and stand by their word.
Why do so many believers struggle with using bad words? Jesus taught, "The good person out of the good treasure of his heart produces good, and the evil person out of his evil treasure produces evil, for out of the abundance of the heart his mouth speaks" (Luke 6:45). In other words, garbage in, garbage out. To change the words that come out of our mouth, we need to change the words that go into our ears.
Many methods can be used to help. First, stop or limit media that uses vulgar language. Movies, television, books, music, articles, comics, and video games that include bad language contribute to much of the negative input we receive.
Second, spend less time around people using bad language. We are called to help reach those without Christ, including those who use bad language. However, if this is a problem area, you may need to decrease how much time you spend in such conversations.
Third, replace bad words with better words. Instead of the word that usually comes to mind, practice replacing it with something else.
Fourth, practice the teaching of James: "Know this, my beloved brothers: let every person be quick to hear, slow to speak, slow to anger" (James 1:19). Think before you speak. As Paul wrote, in your anger do not sin (Ephesians 4:26). These practical and biblical tips can help you better focus on words that build up others and bring glory to God.
Source: Compelling Truth