Before anything else, a necessary observation about the word worthless, because it can wound whoever reads it quickly. The text isn't saying any human being is worthless before God, and the whole Gospel says otherwise. The word describes what that life produces and how much that person's word is worth: it's people from whom nothing good is harvested, and whose guarantee guarantees nothing. It's a judgment about conduct, not a sentence on the soul.
With that caveat made, look at the verb, because that's where the weight of the verse lives: goes about. It doesn't say they lied, or that they lied once in a hard situation. It says goes about with a corrupt mouth, which is the way to describe someone who no longer even makes an effort to lie.
Reflection
1There's a Line, and It's Thin
Everybody has lied at some point. The kid who broke the vase, the adult who invented traffic to explain being late, the professional who said the file was almost ready. If the verse were talking about that, it would be describing all of humanity, instead of a specific kind of person.
The difference is in the relationship a person has with the lie. There's the person who lies and feels bad about it, chewing it over, wanting to go back and fix it. And there's the person who lies and feels nothing, because the lie has become just another tool in the box, next to the phone and the spreadsheet.
The line between the two is thin, and it's crossed slowly. First the person lies and justifies it. Then they lie and get used to it. Then they lie and don't even remember lying, because they no longer register it as a lie, they register it as a way to solve things. When it reaches that point, the problem has stopped being an act and become a character.
2The Lie Has a Body and an Accomplice
The next verse describes a curious scene: "who winks maliciously with his eye, signals with his feet and motions with his fingers" (6:13). Notice the detail, because it's brilliant. Winking isn't the language of someone lying alone, it's a signal arranged in advance. Whoever winks is letting someone know they're in on it.
This dismantles the idea that lying is a solitary sin. It almost always needs a small network: someone who backs up the story, someone who changes the subject at the right moment, someone who doesn't contradict it. And almost everybody has been that second person at some point, the one who didn't lie, just stayed quiet while the lie was being told right in front of them.
And verse 14 completes the picture, saying this person "always stirs up conflict." That's a precise description. Whoever lives off lying needs a murky environment to operate in, because in clarity their story doesn't survive. Where everything is confused, nobody can check anything, and that's exactly where they work best.
3The Problem Isn't in the Mouth
Here's the turn of the day, and it comes from Jesus. He said: "For the mouth speaks what the heart is full of." And he added an image of inventory: "The good man brings good things out of the good stored up in him, and the evil man brings evil things out of the evil stored up in him."
Hold on to the word stored up. The mouth doesn't manufacture anything, it only delivers what was already kept. That's why controlling the mouth is an effort that works for a while and fails under pressure, because on the day of the scare, the exhaustion, or the anger, out comes what was stockpiled, with no filter in between.
That changes the target of the work. It's no use promising to talk less, it's useful to ask what you've been storing up. What you consume, who you talk to, what you let in without reviewing it, all of that goes into the storehouse, and one day the storehouse opens.