John Calvin Commentary Psalms 64:3

"Who have whet their tongue like a sword, And have aimed their arrows, even bitter words," — Psalms 64:3 (ASV)

For they have whetted their tongue like a sword. His enemies, in their rage, aimed at nothing less than his life; yet, what he complains of more than anything else is the poison with which their words were imbued. It is probable that he refers to the slanderous reports which he knew were falsely spread to discredit him, and with the aim of damaging his reputation with the people.

He compares their tongues to swords, and their bitter and venomous words to arrows. And when he adds that they shoot against the upright and innocent, he should be understood as contrasting his integrity with their unprincipled conduct. It inspired him with confidence in his religious addresses to know that he could clear his own conscience of guilt and that he was the target of undeserved attacks by worthless and abandoned men.

In mentioning that they shoot secretly and suddenly, he refers to the cunning that characterized them. They were not only eagerly determined to cause mischief and intent on watching for their opportunities, but also so expert and quick in their movements that they struck their victim before he could suspect any danger. When we hear that David, who was a man in every respect so much more holy and upright in his conduct than we are, suffered from groundless slanders against his character, we should not be surprised if we are exposed to a similar trial.

This comfort, at least, we always have: that we can turn to God and obtain His defense for the upright cause. He takes particular notice of another circumstance: that they shot their poisoned arrows from their lips without fear, or shame. This self-assured spirit demonstrated a degree of abandoned presumption, as they obstinately persisted in the conduct for which they had been repeatedly detected and renewed their desperate attempts, disregarding all fear of God or worldly shame.