James 3:8

But the tongue can no man tame
Either his own, or others; not his own, for the man that has the greatest guard upon himself, his words and actions; yet, what through pride or passion, or one lust or another in his heart, at one time or another, bolts out vain, idle, angry, and sinful words: and he that does not may be set down for a perfect man indeed: nor can he tame or restrain the tongues of others from detraction, calumnies, backbitings, and whisperings; who say, their lips are their own, and who is Lord over us? no man can, by his own power and strength, tame or subdue his tongue, or restrain it from evils it is habituated to, be it lying, cursing, swearing, or what else: God, by his Spirit, power, and grace, can, and often does, change the note of the curser, swearer, liar, and blasphemer; but no man can do this, though he can tame beasts, birds, serpents, and fishes; which shows the tongue to be worse than anything to be found in the whole compass of nature:

[it is an] unruly evil:
an evil it is, for it is a world of iniquity; and an unruly one, being more so than the horse and mule, which are without understanding, who are kept in and governed, and turned any way by the bit and bridle: but though in nature the tongue is fenced by a double fence of the lips and teeth, this is not sufficient to restrain it; it breaks all bounds, and is not to be kept in by nature, art, or argument: nothing but the grace of God can in any measure govern it, or lay an embargo on it:

full of deadly poison,
which, privately, secretly, and gradually, destroys the characters, credit, and reputation of men; and is of fatal consequence in families, neighbourhoods, churches, and states.