For regular daily Bible readers, you may note two echoes in chapter 20. First are the words of Sheba: “We have no share in David, no part in Jesse’s son! Every man to his tent, O Israel!” This sounds very much like the coming statement of the Israelites at the death of Solomon: “What share do we have in David, what part in Jesse’s son? To your tents, O Israel!” (1 Kings 12:16).
The second echo is in the mention of the woman from the “wise” city of Abel Beth Maacah (the place you go for answers – 2 Samuel 20:18). It should remind you of the wise woman from Tekoa who, at Joab’s insistence, talked David into bringing Absalom back home.
In both cases, a matter of national unity lies at the heart of the stories. Though he could not know it at the time, David’s bringing Absalom back sacrificed the nation for one man, his son. In the story of 2 Samuel 20, one man (Sheba) is sacrificed for the unity of the nation.
Amasa seems like a nice enough chap, but clearly his dillydallying (in David’s mind) imperiled the unity of Israel and that, by Joab’s standards, was a capital offense.
Joab is involved in both cases and though he seems like a cold blooded killer, his allegiance is obviously to the unity of Israel. He made a mistake with Absalom, one he corrected himself and in doing so lost (briefly) his place as commander of David’s forces. But he never walked away.
The unity of God’s people is a serious matter to God. The community of faith must not just seem united, it must be united, and the evidence of such unity must be seen in the care and concern we show to one another, and our dedication to act in the favorable interests of the church community rather than the individual.