Thy tongue reckons up mischiefs David is not to be considered as here venting a flood of reproaches against his adversary, as many who have been unjustly injured are in the habit of doing, merely to gratify a feeling of revenge. He brings these charges against him in the sight of God, with a view to encourage himself in the hopefulness of his own cause: for it is plain that the farther our enemies proceed in the practice of iniquity, they proportionally provoke the anger of the Lord, and are nearer to that destruction which must issue in our deliverance. His object, therefore, is not to blacken the character of Doeg in the estimation of the world, but rather to set before his own eyes the divine punishment which the flagrant offenses he specifies were certain to draw down upon his head. Amongst these he singles out, as more especially worthy of reprobation, the hidden treachery with which he had been chargeable in accomplishing the destruction of the priesthood. Adverting to his secret and malicious information, he likens his tongue to a sharp razor, as elsewhere, Psalm 120:4, the tongues of the wicked are compared to "sharp arrows." It is added, working deceitfully, which words are considered by some as referring to the razor which cuts subtilely, and not with an open wound like a sword; but perhaps they may be construed with more propriety as applying to the tongue, [1] although there can be no doubt of the reason of the comparison. The term vl, balang, in verse fourth, which has been translated destruction, I prefer understanding in the sense of hiding or concealment. He seems to allude to the drawing back of the tongue when we swallow; and under this figure, to describe the deceitfulness of Doeg's words, by which he devoured the unsuspecting and the innocent. [2] The great design of David, as I have already remarked in the preceding verses, is to encourage himself in the hope of deliverance by dwelling upon the extreme character of that wickedness which his enemy had displayed.

Footnotes

1 - According to the first sense, the meaning is, that as a razor cuts so easily, that the wound is at first hardly perceptible, in the same manner, the deceitful tongue works its purposes of mischief before the objects which it means to ruin are conscious of their danger. It is like a sharp razor, that cuts the throat before a man is aware of it. "If, however, we take the words, thou workest deceitfully, as being descriptive not of the razor but of the tongue, the sense will be, that such a tongue is capable of inflicting deep and dreadful wounds like a sharp razor." -- Walford.

2 - "vl, balang, is to swallow, to devour, with the idea of eagerness, greediness." -- Gesenius

Thy tongue deviseth mischiefs - The word rendered "mischiefs" means
(a) desire, cupidity: Proverbs 10:3; then
(b) fall, ruin, destruction, wickedness: Psalm 5:9; Psalm 38:12.
The meaning here is, that he made use of his tongue to ruin others. Compare Psalm 50:19. The particular thing referred to here is the fact that Doeg sought the ruin of others by giving "information" in regard to them. He "informed" Saul of what Ahimelech had done; he informed him where David had been, thus giving him, also, information in what way he might be found and apprehended. All this was "designed" to bring ruin upon David and his followers. It "actually" brought ruin on Ahimelech and those associated with him, 1-Samuel 22:17-19.
Like a sharp razor - See the notes at Isaiah 7:20. His slanders were like a sharp knife with which one stabs another. So we stay of a slanderer that he "stabs" another in the dark.
Working deceitfully - literally, making deceit. That is, it was by deceit that he accomplished his purpose. There was no open and fair dealing in what he did.

Deviseth mischiefs - Lies and slanders proceeding from the tongue argue the desperate wickedness of the heart.
Like a sharp razor, working deceitfully - Which instead of taking off the beard, cuts and wounds the flesh; or as the operator who, when pretending to trim the beard, cuts the throat.

Thy tongue deviseth (b) mischiefs; like a sharp razor, working deceitfully.
(b) Your malice moves you by crafty flattery and lies to accuse and destroy the innocents.

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, 1-Samuel 22:9; so antichrist devises mischiefs against the saints of the most High, to wear them out, and thinks to change times and laws, Daniel 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, Psalm 57:4; see Jeremiah 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.

tongue--for self.
mischiefs--evil to others (Psalm 5:9; Psalm 38:12).
working deceitfully-- (Psalm 10:7), as a keen, smoothly moving razor, cutting quietly, but deeply.

Deviseth - Expresses what thy wicked mind had devised. Deceitfully - Doeg pretended only to vindicate himself from disloyalty, 1-Samuel 22:8, but he really intended to expose the priests, to the king's fury.