8 When they were at the great stone which is in Gibeon, Amasa came face to face with them. Now Joab had on his war-dress, and round him a band from which his sword was hanging in its cover; and while he was walking, it came out, falling to the earth.
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.