“The good man out of the good treasure of his heart brings forth what is
 good; and the evil man out of the evil treasure brings forth what is evil;
 for his mouth speaks from that which fills his heart.”  Luke 6:45

In this Scripture we can see that the heart is the center of life, this being so, there are certain things to be considered and the words we speak. 

*The heart should be carefully guarded:
“Keep your heart with all diligence,
 For out of it spring the issues of life.”  Proverbs 4:23

*The heart determines character:
“For as he thinks in his heart, so is he.”  Proverbs 23:7

*The heart is a source of evil:
Explaining to Peter what He said to the multitude that offended the Pharisees, Jesus said,
“Do you not yet understand that whatever enters the mouth goes into the 
 stomach and is eliminated?”
 But those things which proceed out of the mouth come from the heart, and
 they defile a man.”  Matthew 15:17-18
(Read the whole account Vs. 1-20)

*Our opening verse tells us that the heart controls speech.  Read it again.

*The heart is the source of faith:
“For with the heart man believes, resulting in righteousness, and with the
 mouth he confesses, resulting in salvation.”  Romans 10:10

Our opening verse states ‘for his mouth speaks from that which fills his heart’, so looking at the words of the good man, Scripture tells us in 
Proverbs 16:23,
“The heart of the wise teaches his mouth
 And adds learning to his lips.”  

Now then considering wise words we see that--
*They are forcible:
“How forceful are right words!”  Job 6:25a

“A word spoken in due season, how good it is!”  Proverbs 15:23b

*They are pleasant:
“Pleasant words are like a honeycomb,
 Sweetness to the soul and health to the body.”  Proverbs 16:24

*They are appropriate:
“A word fitly spoken is like apples of gold
 In settings of silver.”  Proverbs  25:11

*They are gracious:
“The words of a wise man’s mouth are gracious,
 But the lips of a fool shall swallow him up.”  Ecclesiastes 10:12

*They are comforting:
“The LORD God has given Me 
 The tongue of the learned,
 That I should know how to speak
 A word in season to him who is weary…”  Isaiah 50:4

Scripture gives us warning against an evil heart and evil speaking:
“Beware, brethren, lest there be in any of you an evil heart of unbelief in
 departing from the living God;
 But exhort (encourage) one another daily…”  Hebrews 3:12-13

“Let all bitterness and wrath and anger and clamor and slander be put 
 away from you, along with malice.
 Be kind to one another, tenderhearted, forgiving one another, as God in
 Christ forgave you.”  Ephesians 4:31-32 

“Whoever desires to love life and see good days, 
 Let him keep his tongue from evil and his lips from speaking deceit;
 Let him turn away from evil and do good; let him seek peace and pursue it.
 For the eyes of the Lord are on the righteous, and his ears are open to their   
 prayer.
 But the face of the Lord is against those who do evil.”  1 Peter 3:10-12

I would encourage all of us to do a heart search spiritually and Scripturally that we may be, say and do those things that bring honor and glory to our awesome Lord.  Amen