One of Joab's men, left there on purpose to deliver the following message. He that favoureth Joab; he that would have Joab to be general, rather than such a perfidious rebel and traitor as Amasa. He that is for David; he that wisheth David good success against Sheba, and against all rebels; whereby he implies that though this fact of his was done against the king's command, yet it was for his interest and defence.
Related Commentaries of 2 Samuel 20:11
2 Samuel 20:11
11 And one of Joab's men stood by him, and said, He that favoureth Joab, and he that is for David, let him go after Joab.