What does 2 Samuel 19:13 mean?

'And say to Amasa, “Aren’t you my own family too? From now on, you’ll be my army commander instead of Joab, or may God punish me.”' 2 Samuel 19:13 - Modern Text Bible

(David offers Amasa, who had led Absalom’s army, the top military job, signaling forgiveness and trying to unite the people.)