Absalom had put Amasa in command of the army in the place of Joab. Amasa was the son of Jether the Ishmaelite; his mother was Abigail, the daughter of Nahash and the sister of Joab's mother Zeruiah.)
David also told them to say to Amasa, “You are my relative. From now on I am putting you in charge of the army in place of Joab. May God strike me dead if I don't!”