Some scripture and commentary from a Christian online.
2 Peter 3:10-13
10 But the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up.
11 Seeing then that all these things shall be dissolved, what manner of persons ought ye to be in all holy conversation and godliness,
12 Looking for and hasting unto the coming of the day of God, wherein the heavens being on fire shall be dissolved, and the elements shall melt with fervent heat?
13 Nevertheless we, according to his promise, look for new heavens and a new earth, wherein dwelleth righteousness.
Ephesians 4:
29 Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers...
James 3:9-12
9 Therewith bless we God, even the Father; and therewith curse we men, which are made after the similitude of God.
10 Out of the same mouth proceedeth blessing and cursing. My brethren, these things ought not so to be.
11 Doth a fountain send forth at the same place sweet water and bitter?
12 Can the fig tree, my brethren, bear olive berries? either a vine, figs? so can no fountain both yield salt water and fresh.
James makes it clear that the lives of Christians—the “brothers”—should not be characterized by evil speech. By making the analogy of both salt water and fresh water coming from the same spring (which is uncharacteristic of springs), he makes the point that it is uncharacteristic for a believer to have both praise and cursing come from his/her mouth. Nor is it characteristic for us to praise God on one hand and curse our brothers on the other. This, too, is uncharacteristic of a true believer.
Jesus explained that what comes out of our mouths is that which fills our hearts. Sooner or later, the evil in the heart comes out through the mouth in curses and swearing. But when our hearts are filled with the goodness of God, praise for Him and love for others will pour forth. Our speech will always indicate what is in our hearts. “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).
Why is it a sin to cuss / swear / curse? Sin is a condition of the heart, the mind, and “the inner man” (Romans 7:22), which is manifested in our thoughts, actions and words. When we swear and curse, we are giving evidence of the polluting sin in our hearts that must be confessed and repented of. Thankfully, our great God is “faithful and just and will forgive us our sins and purify us from all unrighteousness” (1 John 1:9). When this happens, we receive a new nature from God (2 Corinthians 5:17), our hearts are transformed, and our speech reflects the new nature God has created within us.....
I will add this scripture that I that comes to mind :
1st Corinthians 15:
33 Be not deceived: evil communications corrupt good manners.
34 Awake to righteousness, and sin not; for some have not the knowledge of God: I speak this to your shame.
