Q. What does Prov 18:20-21 mean? What is it trying to teach us?
A. Although I prefer literal translations for accuracy, this is where an amplified (AMP) or expanded Bible (EXB) can help. I have listed the NASB first, then others to bring out the meaning:
• NASB With the fruit of a man’s mouth his stomach will be satisfied; he will be satisfied with the product of his lips.
• AMPC A man’s [moral] self shall be filled with the fruit of his mouth; and with the consequence of his words he must be satisfied [whether good or evil].
• EXB People will be rewarded for what they say [ From the fruit of the mouth of a person is their stomach satisfied]; they will be rewarded by how they speak [the yield/gain of their lips satisfies].
Basically this teaches “You will have to live with the consequences of everything you say.” GNT
• NASB Death and life are in the power of the tongue, and those who love it will eat its fruit.
• AMP Death and life are in the power of the tongue, And those who love it and indulge it will eat its fruit and bear the consequences of their words.
• EXB What you say can mean [ In the power of the tongue are] life or death. Those who speak with care [love it] will be rewarded [eat its fruit].
The basic teaching is “What you say can preserve life or destroy it; so you must accept the consequences of your words.” GNT
Essentially the two verses teach the same thing, only using different words.