8 When they were at the great stone which is in Gibeon, Amasa came to meet them. And Joab was girded with his apparel of war that he had put on, and thereon was a girdle with a sword fastened upon his loins in the sheath thereof; and as he went forth it fell out.
Matthew Henry's Commentary on 2 Samuel 20:8
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.