How will the kings grow wise?
Rashi: Nevi'im of Yisrael are merciful. They rebuke nations to repent from their evil, for Hashem stretches out His hand to Resha'im and Tzadikim.
Radak: David tells the kings who come to fight him, be wise - you cannot nullify Hashem's act. He decreed that I be king! How can you gather against Him?!
What Musar should they take?
Radak: If until now you were foolish and had evil intent, grow wise and be chastised, and do not elevate [yourselves].
Malbim: Since Hashem authorized me to destroy nations, why should you rebel and wait until you perish? Take Musar via arousal of intellect and accept it from love, or at least due to Musar and fear of punishment that will come on you.
