Charles Ellicott Commentary 2 Samuel 19:23

"And the king said unto Shimei, Thou shalt not die. And the king sware unto him." — 2 Samuel 19:23 (ASV)

The king swore to him. —This oath of David assuring immunity to Shimei brings to mind his dying charge to Solomon concerning him (1 Kings 2:8–9): His hoar head bring thou down to the grave with blood. The whole transaction is to be viewed from a political point. Shimei had been guilty of high treason during David’s distress; upon David’s return, Shimei confessed his fault and exerted himself to help restore David to the throne. He had accordingly been pardoned, and David, somewhat rashly, had confirmed this pardon with an oath, in such a way that he was unable to punish any subsequent treasonable tendencies that Shimei showed.

From the man's character, however, and from Solomon’s address to him (1 Kings 2:44), it is plain that he remained thoroughly disloyal. David saw this and, hindered by his oath from treating him as he deserved, pointed out the case to Solomon. Solomon settled the matter by a compact (into which Shimei willingly entered) that his life would be forfeited whenever he went out of Jerusalem. There he was under supervision; elsewhere he could not be trusted. After a few years, he violated this condition and was executed. David had made a rash oath and observed it to the letter, but no further, towards a thorough traitor.