Ephesians 4:29

Let no corrupt speech proceed out of your mouth, but such as is good for edifying as the need may be, that it may give grace to them that hear.

The Christian is an ambassador at all times of the faith which he has professed. All conversation provides an opportunity of imparting grace to people who might stand desperately in need of it; and for the child of God to waste the vast majority of all such occasions through idle, frivolous, empty, meaningless conversation is a standing tragedy on earth. And what is even worse is the indulgence of conversation which is vulgar, profane or obscene.

That it may give grace ... The Christian should never lose sight of the sad fact of a world lost in sin, without the Lord, needing some word, some ray of light, some word of grace that will point to the Lamb of God that takes away sin.