Whoever of you loves life and desires to see many good days, keep your tongue from evil and your lips from speaking lies.
(Ps. 34:12-13)
The Bible says the first area of our lives that should reflect the presence of God is our speech.

I often joke that some of us should stop asking God for power to raise the dead and start asking Him for power to close our mouths.
He who guards his mouth and his tongue,” the Bible says, “keeps himself from calamity.
(Prov. 21:23)
“Calamity” is a strong word. It means to be stricken physically, financially, emotionally and mentally. Many Christians suffer calamity because their tongues are out of control and God is letting them eat the fruit of it. They may be saved, but they’re certainly not happy.

When we’re not feeling well and we go to the doctor, he says, “Let me see your tongue.” His trained eye can spot the diseases of the body through the evidence of the tongue.

When we come to God in prayer, He says, “Let Me see your tongue.” He can spot the stains of criticism, of faultfinding, of gossip and slander.

We should only criticize when we can do so with justice, with kindness and with humility, for the purpose of solving a problem and not attacking a person. To criticize in any other way is to hurt others and ourselves.

In the same way, we should learn to ignore some criticisms and to welcome others. In doing so, we will take an adversity and convert it to an asset and learn more deeply how to be happy in an unhappy world.

Source: 
Being Happy in an Unhappy World by John Hagee.
Excerpt permission granted by John Hagee Ministries