Commentaries
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.
9. took Amasa by the beard with the right hand to kiss him—This act, common with two friends on meeting when one of them returns from a journey, indicates respect as well as kindliness, and the performance of it evinced the deep hypocrisy of Joab, who thereby put Amasa off his guard. No wonder, then, that while this act of friendly gratulation after long absence occupied Amasa's attention, he did not perceive the sword that was in Joab's left hand. The action of Joab was indeed a high compliment, but neither suspicious nor unusual and to this compliment, Amasa paying attention and no doubt returning it with suitable politeness, he could little expect the fatal event that Joab's perfidy produced.