The Master says this:
But I say unto you, That every idle word that men shall speak, they shall give account thereof in the day of judgment. For by thy words thou shalt be justified, and by thy words thou shalt be condemned.
(Matthew 12:36-37)
What constitutes an idle word? It can’t possibly mean “pointless” as some interpretations put it. “Careless” is perhaps the most common translation of the word, but I don’t think it goes far enough in explaining the point Jesus is making in this context. Careless words are just words we say without thinking. I would hope words said in casual conversation, said without much thought before or after they are uttered, are not piling up as a list of crimes condemnable against me. I talk a lot, and not everything I say is important or necessarily said with great care or forethought. I like to shoot the breeze and talk about nothing as much as the next person. I don’t think that’s Jesus’ point, fortunately. “Careless” is the start of the thought, but it doesn’t go far enough. I think “dismissive” is a better translation. There’s carelessness in a dismissive attitude, but not every careless word is dismissive of the one being spoken to (or about).
In this context, Jesus had just healed a man, and in response, the hard-hearted Pharisees attempted to dismiss the Lord’s power by saying “He only casts out demons by the power OF the demons” (Matthew 12:22-24). Instead of considering how wrong they had been about Jesus, they doubled-down in arrogance and stubbornness and tossed out an asinine theory that Jesus was actually an agent of the Devil working against the Devil. Their words were “idle.” They were lazy, thoughtless, harmful, and dismissive.
The Pharisees had already made up their minds about Jesus, and so nothing He did was going to convince them they were wrong. They proved that by witnessing a miracle before their very eyes and then just shrugging and coming up with a half-baked explanation about why it didn’t matter.
If your heart is hard, nothing I say or do can change that. If you’ve already made up your mind and you don’t want to change it, you will believe any lie, convince yourself of any foolish notion, and twist common sense, logic, and the obvious truth into pretzeled knots to keep on believing what you already want to believe, or to keep pressing on to do what you’ve already decided you were going to do.
Beware. Those idle words you say—to convince yourself or others to believe a lie, or to do something against your conscience—will come back against you. You will give an account of those idle words, of every idle word, in the day of Judgment.
~Matthew