10 But Amasa did not observe the sword that was in Joab's hand. So Joab struck him with it in the stomach and spilled his entrails to the ground without striking a second blow, and he died. Then Joab and Abishai his brother pursued Sheba the son of Bichri. 11 And one of Joab's young men took his stand by Amasa and said, "Whoever favors Joab, and whoever is for David, let him follow Joab." 12 And Amasa lay wallowing in his blood in the highway. And anyone who came by, seeing him, stopped. And when the man saw that all the people stopped, he carried Amasa out of the highway into the field and threw a garment over him. 13 When he was taken out of the highway, all the people went on after Joab to pursue Sheba the son of Bichri.
Matthew Henry's Commentary on 2 Samuel 20:10-13
Commentary on 2 Samuel 20:4-13
(Read 2 Samuel 20:4-13)
Joab barbarously murdered Amasa. The more plot there is in a sin, the worse it is. Joab contentedly sacrificed the interest both of the king and the kingdom to his personal revenge. But one would wonder with what face a murderer could pursue a traitor; and how, under such a load of guilt, he had courage to enter upon danger: his conscience was seared.