Charles H. Spurgeon on Psalms 64:3

Who whet their tongue like a sword. Slander has ever been the master weapon of the good man's enemies, and great is the care of the malicious to use it effectively. As warriors grind their swords, to give them an edge which will cut deep and wound desperately, so do the unscrupulous invent falsehoods which shall be calculated to inflict pain, to stab the reputation, to kill the honour of the righteous. What is there which an evil tongue will not say? What misery will it not labour to inflict? And bend their bows to shoot their arrows, even bitter words. Far off they dart their calumnies, as archers shoot their poisoned arrows. They studiously and with force prepare their speech as bent bows, and then with cool, deliberate aim, they let fly the shaft which they have dipped in bitterness. To sting, to inflict anguish, to destroy, is their one design. Insult, sarcasm, taunting defiance, nicknaming, all these were practised among Orientals as a kind of art; and if in these Western regions, with more refined manners, we are less addicted to the use of rough abuse, it is yet to be feared that the less apparent venom of the tongue inflicts none the less poignant pain. However, in all cases, let us fly to the Lord for help. David had but the one resource of prayer against the twofold weapons of the wicked, for defence against sword or arrow he used the one defence of faith in God.