This is deadly language. God does not fool around with sin. God promises swift and definite judgment to all who practice evil against people like his servant David. Since evil-doers are pregnant with evil, God must be pregnant with His judgment of them. He repays evil with judgment.
David points out that God is actively judging, even today, for God expresses his wrath every day. God is not asleep. He did not create the world and then turn His back upon it. He is intimately concerned with and involved in the goings-on of His creation. This is the doom of those who don’t repent of sin.
What would cause God to relent in His judgment? God’s mercy on the repentant.
Throughout the Bible, God’s mercy on the repentant is taught and demonstrated: He was going to destroy Nineveh, but they repented so He had mercy on them (Jonah 3); David repented from his sins of adultery and murder and God restored His favor (see Psalm 51); the Word of God states: “He who conceals his sin does not prosper, but whoever confesses and renounces them finds mercy” (Prov 28:13) and “Let the wicked forsake his way and the evil man his thoughts. Let him turn to the LORD, and he will have mercy on him, and to our God, for he will freely pardon” (Isa 55:7).
For God, it seems like it is always mercy first, and then judgment. Knowing this, we should imitate God, desiring first and praying for the repentance of our enemies before we pray for their punishment.
So if David’s enemies want mercy, they must repent. And if they don’t, they will have to deal with God’s swords, and bows and arrows. And these are not little weapons but “instruments of death” (vs. 13) He chooses. God will destroy His foes. Make no mistake, the wrath of God will be terrible.