Joab's cruelty

“Joab said to Amasa, ‘How are you, my brother?’ Then Joab took Amasa by the beard wtih his right hand to kiss him. Amasa was not on his guard against the dagger in Joab’s hand, and Joab plunged it into his belly, and his intestines spilled out on the ground. Without being stabbed again, Amasa died.” 2 Samuel 20:9-10
Joab was the leader of David’s army and was fiercely loyal to David. But this loyalty was devoid of morality. Joab killed several people in cold blood – we read of how he killed Amasa here; he also killed his own brother Abner (2 Sam. 3:27), and David’s son Absalom (2 Sam. 18:14). David remembered all this, and told Solomon to deal with Joab in the only way left for him (1 Kin. 2:5). His loyalty was undermined by his cruelty.
There are other cases of this same temperament. Another example is that of Levi and Simeon, the sons of Jacob, in Gen. 34. After Hamor raped their sister Dinah, they deceived the entire town of Shechem into being circumcised, but before they had recovered, Simeon and Levi killed every man in the town. Jacob did not forget about this, and cursed them for it when he was on his deathbed (Gen. 49:5-7).
There are many instances that we face where the end does not justify the means. David was a ‘man of blood’ – a warrior – yet he was also a man after God’s own heart. Joab killed people in cold blood out of envy and revenge. While both were serving their God, king, and country, only one was rewarded.