John Wesley on 2 Samuel 20:10

The sword - Which falling out, as it seemed, casually, he supposed that Joab intended only to put it into its scabbard, and therefore took no care to defend himself against the stroke. So Joab - Who now boldly resumed his former place, and marched in the head of the army. It is not strange, that Amasa's soldiers did not fight to revenge his death; partly, because not many of them were yet come up, as the following verses shew; and partly, because Joab's interest and authority with the military - men was very great; especially, with David's guards, who were here present, and who had no kindness for Amasa, as having been the general of the rebellious army; and, as they might think, not fit to be put into a place of so great trust.