10 But Amasa took no heed to the sword that was in Joab’s hand. So he struck him with it in the body, and shed out his bowels to the ground, and didn’t strike him again; and he died. Joab and Abishai his brother pursued after Sheba the son of Bichri.
Matthew Henry's Commentary on 2 Samuel 20:10
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.