“There are some telltale signs that would be good for every member of the household to be aware of.
Bitterness always has a sharp memory for all the details. And this is because bitterness has good study habits: review, review, review.
It’s also true that bitterness frequently resorts to anonymous critiques or attacks. Bitter words are frequently unsigned. This is obviously more difficult to accomplish inside a home, but sin can be pretty creative.
Hide me from the secret counsel of the wicked; from the insurrection of the workers of iniquity: Who whet their tongue like a sword, and bend their bows to shoot their arrows, even bitter words: That they may shoot in secret at the perfect: suddenly do they shoot at him, and fear not. (Ps. 64:2-4)
Another good indicator is the practice of conducting imaginary conversations in the mind. ‘Then I says to him, says I…” And of course, during these imaginary conversations, the brunt of this brilliant repartee is never capable of coming back with anything intelligible at all.
Bitterness also starts to invert the moral order of things.
Woe unto them that call evil good, and good evil; that put darkness for light, and light for darkness; that put bitter for sweet, and sweet for bitter. (Is. 5:20)
A bitter person frequently starts to approve what they would have never approved at an earlier time in their life. When a Christian finds himself justifying what he would never have approved in other circumstances, he is probably bitter.
As we saw earlier in the passage from Hebrews 12, bitterness is like a root. It grows. It gathers nutrients everywhere it can. Soon the person’s heart and mouth are full of it – ‘Whose mouth is full of cursing and bitterness’ (Rom. 3:14). What happens when the jar of your life is jostled? What comes out? If bitterness splashes on to everyone, this simply tells us what the jar was already full of.”
– Douglas Wilson, My Life for Yours (pp. 44-45)