To determine whether cussing is a “sin,” we need to first discuss what sin is and second define what cursing, swearing, or cussing is.
The Bible tells us that sin is the transgression of the law (1 John 3:4) and rebellion against God (Deuteronomy 9:7, Joshua 1:18). It is furthermore described as imaginations of the unrenewed heart (Genesis 6:5, 8:21), defiling (Proverbs 30:12, Isaiah 59:3), disgraceful (Proverbs 14:34), and unrighteous (1 John 5:17), among other things.
Cursing is our way of describing words that are--for the most part--culturally or socially unacceptable. It is a slippery slope, however, to define a curse word because words are always taking on new meanings. Some curse words in the English language are actually authorized words to describe authentic things but have taken on a new meaning as time has progressed. Because of this, it is nearly impossible to create a canonized list of words that are considered curses. Nevertheless, it can be concluded that there are words that are purely crude or demeaning and are, therefore, unequivocally curse words.
It needs to be understood that cursing can also include any verbal expression of a word that may not necessarily be considered a traditional curse word. This means that the understanding of cursing needs to be expanded to not only include culturally or socially unacceptable words but also any word that is used to demean another individual or express extreme dissatisfaction with a particular situation, especially when that dissatisfaction is directed toward God. Christians are often guilty of substituting more culturally acceptable words in place of unacceptable words to describe their dissatisfaction with a situation or even in reference to an individual. These are called euphemisms and cannot be considered justified alternatives.
Scripture has much to say about how Christians ought to use their tongues. Jesus specifically taught that what comes out of a man’s mouth is evidence of what is in his heart. Luke 6:45 says, “The good man out of the good treasure of his heart brings forth what is good; and the evil man out of the evil treasure brings forth what is evil; for his mouth speaks from that which fills his heart.”
Paul wrote in Ephesians 4:29, “Let no corrupt word proceed out of your mouth, but what is good for necessary edification, that it may impart grace to the hearers.” John MacArthur has written of this verse, “The word for ‘corrupt’ refers to that which is foul or rotten, such as spoiled fruit or putrid meat. Foul language of any sort should never pass a Christian’s lips, because it is totally out of character with his new life in Christ.” The final portion of the verse offers a worthy use of our tongue--"what is good for edification.”
James gives us three illustrations from nature to demonstrate the sinfulness of cursing: “With [our tongue] we bless our Lord and Father, and with it we curse men, who have been made in the likeness of God; from the same mouth come both blessing and cursing. My brethren, these things ought not to be this way. Does a fountain send out from the same opening both fresh and bitter water? Can a fig tree, my brethren, produce olives, or a vine produce figs? Nor can salt water produce fresh,” (James 3:9-12).
Finally, 1 Peter 3:10 says, “For He who would love life and see good days, let him refrain his tongue from evil and his lips from speaking deceit.”
We can conclude that from the Biblical definition of sin, our overview of cursing and Scripture’s many expressions on the use of our tongue is without question a sin to curse. As Christians, we are expected to rest on the promises of God, “cleansing ourselves from all defilement of flesh and spirit, perfecting holiness in the fear of God” (2 Corinthians 7:1). Cursing is contrary to resting on God’s promises, for it is a failure to follow the Lord’s greatest commandments--to love God and to love people (Matthew 22:37-40). When we curse an individual, we do not love people, and when we curse God, we do not love Him. Thankfully, God forgives us of our sins through the redemption found only in Jesus Christ (John 3:16).