Proverbs 15:28
The heart of the righteous ponders how to answer,
but the mouth of the wicked pours out evil things.
Note the contrast between the heart of the righteous and the mouth of the wicked. Jesus says that it is out of the heart that evil things pour out. Evil pours out of a heart filled with evil. Evil pours out also because the unrighteous heart fails to check itself. It simply acts naturally, which is very easy to do in our society that teaches the principle, trust your heart above all else.
The righteous ponders how to answer. He looks within himself. He considers his motivations. He thinks about what is right, specifically what is pleasing to God. The process of pondering gives him time to guard his heart and not to give vent to the sinful dispositions within.
Our heart is capable of all kinds of sin. But in the heart of the righteous is the new man born of Christ and indwelt by the Holy Spirit. If we give attention to the Spirit within us, we will not grieve the Spirit with our thoughtless speech and behavior. Think before you speak today. Better yet, pray before you speak. Ask the Spirit for wisdom; ask the Lord to protect your heart so that you will honor him with your words.