Then David said to the young man who had brought the news, “Where are you from?” And he replied, “I am a foreigner, an Amalekite, who lives in your land.” 

“Why were you not afraid to kill the LORD’s anointed one?” David asked. Then David said to one of his men, “Kill him!” So the man thrust his sword into the Amalekite and killed him. “You have condemned yourself,” David said, “for you yourself confessed that you killed the LORD’s anointed one.”

2 Samuel 1:13-16

Now the Philistines attacked Israel, and the men of Israel fled before them. Many were slaughtered on the slopes of Mount Gilboa. The Philistines closed in on Saul and his sons, and they killed three of his sons—Jonathan, Abinadab, and Malkishua. The fighting grew very fierce around Saul, and the Philistine archers caught up with him and wounded him severely.
1 Samuel 31:1-3

• David was both loyal to Saul and brutal within ancient Near Eastern culture.
• “In this period it was common for captured kings to be mutilated and subjected to a life of humiliation. Putting out the eyes or cutting off the thumbs and big toes were just a few of the procedures used. As a sign of their ignominy, they were doomed to spend miserable years fighting for scraps under the triumphant king’s table, or displayed in public places for what abuse passersby might invent. Tortuous practices were continued by the Babylonians, Assyrians and Persians, and the literature is full of gruesome acts performed on captured enemies. Other examples of a king requesting his armor bears kill him exist in Assyrian records. The Elamite king and his armor bearer stabbed each other simultaneously.” IVP Bible Background Commentary
• A king’s head was a treasured prize of conquest.
• A dismembered unburied body was a disgrace and shame for the victim and the family and nation. 
• Impaling bodies was a common tactic used by armies of the ancient Near East.
• David had just finished battling the Amalekites, so the arrival of an Amalekite messenger may not have been welcome.
• David maintained strict loyalty to Saul and saw the Amalkite’s act (even though he was lying) as traitorous. 

We can uphold honor and loyalty like David, but with a heart of love and peace.