2 Samuel 19:13

Flesh? Amasa was his nephew, and as he had been appointed general by Absalom, his influence would be the greatest to bring back those who had given into the delusion. A sense of his misconduct would also render him more humble, and easier to manage than Joab, whose insolence caused him to be insupportable to the king. David designed to transfer the authority of the latter, (Calmet) which he had now enjoyed 23 years, since the taking of Sion. David's promise did not oblige him to keep Joab in that office for life, if his conduct should prove unsatisfactory. Hence he appointed Amasa to pursue the rebels, and afterwards Abisai, setting Joab aside. But the haughty warrior supplanted both, and retained the command, as it were in spite of his sovereign, chap. xx. 4, 15., &c. (Haydock)