John Calvin Commentary Psalms 109:3

"They have compassed me about also with words of hatred, And fought against me without a cause." — Psalms 109:3 (ASV)

And they have encompassed me. He complains that from all quarters he was assailed with the most hostile and abusive epithets, and this, most undeservedly. And, using a beautiful comparison, he shows that the tongues of his enemies were so full of deadly poison that it was harder for him to endure their attacks than those of a great army, and all the more so because he deserved no such treatment from them.

This type of warfare, to which God very frequently summons his children, must be carefully considered by us. For though Satan may assault them with open violence, yet since he is the father of lies, he endeavors, with the amazing dexterity he possesses in heaping calumny upon them, to tarnish their reputation, as if they were the most depraved of mankind.

Now, just as what was prefigured by David was fulfilled in Christ, so we must remember that what is lacking in the afflictions of Christ is daily being filled up in believers (Colossians 1:24); because he, having once suffered in himself, calls them to be sharers and associates with him in his sufferings.