For whatever is in your heart determines what you say.  A good person produces good words from a good heart, and an evil person produces evil words from an evil heart.
And I tell you this that you must give an account on Judgment Day of every idle word you speak.  The words you say now reflect your fate then: either you will be justified by them or you will be condemned. Matthew

We all make many mistakes, but those who control their tongues can also control themselves in every other way.  We can make a large horse turn around and go wherever we want by means of a small bit in its mouth.  And a tiny rudder makes a huge ship turn wherever the pilot wants it to go, even though the winds are strong.  So also, the tongue is a small thing, but what enormous damage it can do.  A tiny spark can set a great forest on fire.   And the tongue is a flame of fire.  It is full of wickedness that can ruin your whole life.  It can turn the entire course of your life into a blazing flame of destruction, for it is set on fire by hell itself.

People can tame all kinds of animals and birds and reptiles and fish, but no one can tame the tongue.  It is uncontrollable evil, full of deadly poison.  Sometimes it praises our Lord and Father, and sometimes it breaks out into curses against those who have been made in the image of God.  And so blessing and cursing come pouring out of the same mouth.  Surely, my brothers and sisters, this is not right!  Does a spring of water bubble out with both fresh water and bitter water?  Can you pick olives from a fig tree or figs from a grapevine?  No, and you can’t draw fresh water from a salty pool. James