Although Christians are not going to live like the rest of the world, it does not mean they are completely free from sin and one of the worst problems is the mouth. James 3:5-6 warns that the tongue is such a small part of the body yet it causes the greatest of harm. Some Christians may be showing fruits of true conversion like continued repentance, good works and desire for fellowship but they still have to fight the problem of hypocrisy. This quote by the great Protestant preacher Harry Ironside means a lot and many Christians do have a problem with their mouth even if the greater sins repel them, they take no pleasure in sin but they have their tendency to have a big mouth.
One of the greatest rebukes that a godly preacher can give is, "We can see you are a Christian with your continued repentance, you love doing good and you don't take credit for it but you watch your mouth." Many Christians can be guilty of preaching but with an inconsistent life. Some Christians may even have the problem of engaging in some form of gossip, overly harsh speech or tactless behavior. Even if the Christian shows disdain for sin as a result of salvation, they can end up sinning a lot with the mouth which can result to chastisement from God.
I am also reminded of Dr. John F. MacArthur's quote from his book Hard to Believe saying, "Don’t believe anyone who says it’s easy to become a Christian. Salvation for sinners cost God His own Son; it cost God’s Son His life, and it’ll cost you the same thing. Salvation isn’t gained by reciting mere words. Saving faith transforms the heart, and that in turn transforms behavior. Faith’s fruit is seen in actions, not intentions. There’s no room for passive spectators: words without actions are empty and futile. Remember that what John saw in his vision of judgment was a Book of Life, not a book of Words or Book of Intellectual Musings. The life we live, not the words we speak, reveals whether our faith is authentic."
What Christians need to remember is that when it comes to the power against sin, remember what David wrote in Psalm 141:3 saying, "Set a watch, O LORD, before my mouth; keep the door of my lips." Every Christian must realize that change comes through repentance of sin, that change is daily and it is not instantaneous. The only real power against sin is not the Christian himself or herself but by the very grace of God. Titus 2:11-14 is clear that it's God's grace that brings a new life to the Christian. 1 Corinthians 6:11 teaches sanctification is also the work of God and not just salvation. The only real power against one's mouth's sins is still in the Lord Jesus Christ and no other.