A godly mouth can be a great blessing to anyone who has one granted to him by the grace of God. Such a mouth, though given by God, must be disciplined to follow Him only - and not the foolishness of the natural man.
The wisdom of God is found on a certain kind of man. He is called a discerning man. The Hebrew word used here is "bin" and it speaks of someone who through the use of the Scriptures is able to determine the difference between what is of God and what is not. This discerning heart and mind instructs the lips of the wise man. We learn later in verse 14 that this man stores up knowledge. This knowledge is a practical knowing of God and of the world that is around him. Thus this wise man instructs his mouth with this knowledge. He learns to know much, but not always speak what he knows. He has learned that he can NOT say things and be a blessing. Thus he seeks to quell within himself words and statements that will unnecessaily disburb the peace in relationships. Many an argument and fight could be prevented if one or the other of the two combatants would have practiced this wisdom. They would keep their words to themselves - knowing that sharing their "knowledge" would be done more from pride than from love. We know from the New Testament that knowledge puffs up - but love edifies. We can share all our knowledge - and by doing so cause a disturbance as others react to our pride. The wise man stores up knowledge within - and only brings that knowledge out at the direction of the Holy Spirit - Who will direct him to use that knowledge to build up and encourage others.
We are also told of the fool - and his mouth. These two verses go together because they speak of the speech of one - and then the consequences of the other. The next verse reverses this order - trading the wise man for the fool in his speech - and the fool for the wise man in the reward or retribution that results. The consequences of the fool is a rod for his back. His words are the source of his punishment - for they evidence his foolishness and lack of regard for what is right. A proverb from the Talmud expresses this wonderfully when we read there, "that which a wise man gains by a hint, a fool only obtains by a club." The wise man learns - instructs his mouth and heart with that wisdom - and therefore avoids problems and public discipline. The fool chooses to let his mouth run - and with that overactive mouth - ruin comes to him.
Biblically we can remember the difference between Solomon and his son, Rehoboam. Solomon began his reign seeking God and requesting wisdom from Him. His son Rehoboam had an opportunity to win over the people - but chose the foolish counsel of his friends. That led him to speak harsh, unkind, oppressive words to the people. In the end he lost all but one tribe - which God granted to him because of His promise to David. But how the foolish mouth granted him much destruction and difficulty. The wise mouth, though, was blessed in many wonderful ways. So take the time to listen - and allow God's wisdom to sink deep enough into your heart so that it instructs your mouth on what to say. Doing this promotes blessing.