Albert Barnes Commentary Micah 6:12

"For the rich men thereof are full of violence, and the inhabitants thereof have spoken lies, and their tongue is deceitful in their mouth." — Micah 6:12 (ASV)

For the rich men thereof - that is, of the city (Micah 6:9)—they are full of violence. It would have been little, had thieves and robbers lived by violence, but now (as Isaiah at the same time upbraids them), her princes were become companions of thieves (Isaiah 1:23). Not the poor out of distress, but the rich, out of wantonness and exceeding covetousness and love of luxury, not only did wrong but were filled, not so much with riches, as with violence. Violence is the very meat and drink with which they are filled, indeed, and with which they shall be filled, when it is returned upon their heads.

And the inhabitants thereof have spoken lies - Fraud is itself lying, and lying is its inseparable companion. Jerome says: “Lying follows the gathering together of riches, and the hard custom to lay up riches has a deceitful tongue.” The sin, he says, is spread throughout all her inhabitants; that is, all of them, as their custom, have spoken lies, and, even when they do not speak, the lie is ready; their tongue is deceitful (literally, deceit) in their mouth.

It is deceit, nothing but deceit, and that, deceit which should overthrow and ruin others. One intent on gain has the lie ever ready to be uttered, even when he does not speak. It lurks concealed, until it is needed.