שמואל ב, פרק ד׳, פסוק ט׳

When individuals attempt to win royal favor through violence, they often deeply misjudge the leader they seek to impress. David's reaction to Rechab and Baanah stems from a profound anger over their conspiracy and act of rebellion. He addresses them with a solemn oath [ביאור שטיינזלץ], declaring that God has rescued his life from all trouble. This powerful statement prepares the ground for his harsh response, which is based on a direct precedent from his past [אברבנאל].

He reminds the brothers of the Amalekite youth who once came to Ziklag claiming to have killed Saul. That young man expected David to view him as a bearer of good news and reward him for the message. However, David understood that the Amalekite had not actually killed Saul on his own initiative. If the youth harmed the king at all, it was only at Saul's own request after he had already fallen in battle and knew he would not survive. The primary reason David executed the Amalekite was his offensive behavior as a messenger, as the young man displayed joy and cheerfulness over the death of God's anointed [אברבנאל].

Driven by this same principle, David now responds with fierce anger toward the brothers. They mistakenly thought they could bring him happiness and win his favor through an act of murder, entirely failing to realize how he would judge their crime.