Proverbs 15 contrasts the heart and mouth of the wise, and the heart and mouth of the wicked. Contrast is a teaching tool of Scripture!
Jesus said, Out of the abundance of the heart, the mouth speaks (Luk 6:45). The heart and mouth are tied together. So if we want to change what comes out of our mouths, we have to change what is in our hearts.
The mouth of the righteous:
speaks softly in the face of wrath and settles contention;
dispenses knowledge and makes knowledge acceptable (accessible);
utters that which is wholesome, which promotes life;
speaks that which is pure, which promotes pleasantness.
I looked up “pure” in Hebrew: it means, clear as opposed to filthy (as in water); unmixed or uncontaminated (as in not mixing seed or unlike fibers); clean as opposed to unclean (in the Levitical sense, as untouched by death or sin).
Purity promotes pleasantness: pleasant means that which delights the LORD (as opposed to that which is abominable to Him); suitable, becoming, as that which increases or enhances beauty; brightness or glory; gracious or favorable. This Hebrew word in the Greek translation of the Old Testament which the Jews made, is the same word used which is translated “grace” in the New Testament.
The heart of the righteous studies how to answer. The righteous take time to plan what they might say, and considers what the most fitting answer might be, while the wicked spews forth the first thing that enters his head.
The mouth of the wicked:
is quick to anger and speaks harsh words that stir up anger;
pours forth foolishness and evil;
utters perverseness: it is crooked, it deceives by flattery or slipperiness, it tells what one wants to hear without caring what is true.
In this chapter, we also learn some things that delight the heart of the LORD, and some things that are abominable to Him:
He is delighted by the prayer of the upright; the words of the pure; the way (manner of life) of the righteous.
He is repulsed by the sacrifice, thoughts, and way (manner of life) of the wicked. If the wicked are offering sacrifices to the LORD, which He hates, then it stands to reason that the wicked are found within the assembly of believers also, whether of Jews or Christians.