John Wesley on 2 Samuel 19:13

Of Joab - Who, besides his other crimes, had lately exasperated the king by his murder of Absalom, contrary to David's express command. And therefore the king having now the opportunity of another person who had a greater interest than Joab, gladly complies with it, that so he might both chastise Joab for his faults, and rescue himself from the bondage in which Joab had hitherto held him.