Jamieson, Fausset and Brown on 2 Samuel 19:16-23

16-23. Shemei ... a thousand men of Benjamin with him--This display of [Shemei's] followers was to show what force he could raise against or in support of the king. Expressing the deepest regret for his former outrageous conduct, he was pardoned on the spot; and although the son of Zeruiah urged the expediency of making this chief a public example, his officiousness was repulsed by David with magnanimity, and with the greater confidence that he felt himself now re-established in the kingdom (see on 1Ki 2:8).