8 As they arrived at the great stone in Gibeon, Amasa met them. Joab was wearing his military tunic with a dagger strapped to his belt. As he stepped forward to greet Amasa, he slipped the dagger from its sheath.

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.