John Gill

Thy tongue deviseth mischiefs,.... Abundance of mischiefs, in a variety of ways, against many persons, even all good men. What properly belongs to the heart is here ascribed to the tongue; because, as Aben Ezra observes, it is the interpreter and discoverer of the thoughts of the heart: out of the abundance of that the tongue speaks and declares the mischief it has devised. Doeg intended mischief to David, when he spoke to Saul, Sa1 22:9; so antichrist devises mischiefs against the saints of the most High, to wear them out, and thinks to change times and laws, Dan 7:25; like a sharp razor, working deceitfully; that is, his tongue was like a razor; the razor is but a small instrument, and the tongue is but a little member: the razor is a sharp and cutting one, and so is the tongue; and therefore compared to a sharp sword, Psa 57:4; see Jer 18:18; the razor takes off the beard cleanly and wholly; Doeg's tongue was the cause of the utter ruin of Ahimelech's family and the city of Nob; and as a razor may be said to "work deceitfully", when it turns aside in the hand of him that useth it, and with the hair takes off more than it should, even skin and flesh, or cuts the man's throat; so in a deceitful and insidious manner did Doeg work the destruction of Ahimelech and the priests of the Lord.