A. Evil speech comes from an evil heart:

PRO 15:2. The tongue of the wise useth knowledge aright: but the mouth of fools poureth out foolishness.

PRO 15:28. The heart of the righteous studieth to answer: but the mouth of the wicked poureth out evil things.

MAT 12:35. A good man out of the good treasure of the heart bringeth forth good things: and an evil man out of the evil treasure bringeth forth evil things.

B. Evil foolish speech corrupts & stinks:

ECC 10:1. Dead flies cause the ointment of the apothecary to send forth a stinking savour: so doth a little folly him that is in reputation for wisdom and honour.

1COR 15:33. Be not deceived: evil communications corrupt good manners.

C. The perverse (polluted) & froward (defiant) tongue:

PRO 8:13. The fear of the LORD is to hate evil: pride, and arrogancy, and the evil way, and the froward mouth, do I hate.

PRO 15:4. A wholesome tongue is a tree of life: but perverseness therein is a breach in the spirit.

PRO 26:18. As a mad man who casteth firebrands, arrows, and death,

PRO 26:19. So is the man that deceiveth his neighbour, and saith, Am not I in sport?

D. Foolishness & vain talk leads to mischief & ungodliness:

PRO 14:7. Go from the presence of a foolish man, when thou perceivest not in him the lips of knowledge.

PRO 15:14. The heart of him that hath understanding seeketh knowledge: but the mouth of fools feedeth on foolishness.

ECC 10:13. The beginning of the words of his mouth is foolishness: and the end of his talk is mischievous madness.

2TIM 2:16. But shun profane and vain babblings: for they will increase unto more ungodliness.

E. An uncontrolled tongue brings disaster:

PSA 109:17. As he loved cursing, so let it come unto him: as he delighted not in blessing, so let it be far from him.

PSA 109:18. As he clothed himself with cursing like as with his garment, so let it come into his bowels like water, and like oil into his bones.

PSA 109:19. Let it be unto him as the garment which covereth him, and for a girdle wherewith he is girded continually.

PSA 109:20. Let this be the reward of mine adversaries from the LORD, and of them that speak evil against my soul.

PRO 10:14. Wise men lay up knowledge: but the mouth of the foolish is near destruction.

PRO 10:10. He that winketh with the eye causeth sorrow: but a prating fool shall fall.

PRO 12:13. The wicked is snared by the transgression of his lips: but the just shall come out of trouble.

PRO 13:3. He that keepeth his mouth keepeth his life: but he that openeth wide his lips shall have destruction.

PRO 17:20. He that hath a froward heart findeth no good: and he that hath a perverse tongue falleth into mischief.

PRO 18:7. A fool's mouth is his destruction, and his lips are the snare of his soul.