Moussar sur Jérémie 9:4

The ninth section: Children who do not lie in recounting things that they heard and telling over events, but switch the words according to the circumstances of their wishes, [yet it is] without hurting any person through it. However they find a little benefit with their lies, even though they do not make money from it. And our Rabbis said (Yevamot 63a) that this is also forbidden, as it is stated (Jeremiah 9:4), “they have trained their tongues to speak falsely.” However their punishment is not like those that lie about something that [did not happen], the nature of which we discussed in the fifth (it should say fourth) section. Behold these are the sections of the group of liers; and we have already mentioned their centrality to you for the ways of faithful people, and that they are fundamental for the soul.

The second is because the repentance of one involved in evil speech is difficult, since he has taught his tongue to speak falsehood, and sent his mouth to evil. From so much habit, he does not control his spirit, and it is as if his mouth causes the thought - like the matter that is stated (Psalms 52:4), “Your tongue devises mischief”; and it is stated (Ecclesiastes 10:12), “but a fool’s lips will swallow him up”; and it is stated.(Proverbs 18:7), “The fool’s speech is his ruin (mechitah).” And mechitah is an expression of fear and trepidation. It means to say that the fool is afraid and in trepidation from the rage of his tongue, lest he be ensnared - like he fears from his enemy - as his lips are not in his control.

There are other liars close to the first group in level [of lying] but not exactly like them. Namely, those who lie in their reports and statements. These peoples' profession is not to go around and make up stories and deeds that never were nor will be. But when they come to tell over something, they mix in whatever lies they happen to think of. They habituate in this until it becomes part of their nature. These are the liars whose word is impossible to believe. This is as what our sages, of blessed memory, said: "it is the penalty of a liar, that even when he tells the truth, he is not listened to" (Sanhedrin 89b). For this evil has ingrained itself in their nature such that their words are unable to leave their mouths free of falsehood. It is about this that the prophet grieved and said: "they have taught their tongue to speak lies, they weary themselves to commit iniquity" (Yirmiya 9:4).