1Joab was told, “The king is weeping and mourning for Absalom.” 2And for the whole army the victory that day was turned into mourning, because on that day the troops heard it said, “The king is grieving for his son.” 3The men stole into the city that day as men steal in who are ashamed when they flee from battle. 4The king covered his face and cried aloud, “O my son Absalom! O Absalom, my son, my son!”
5Then Joab went into the house to the king and said, “Today you have humiliated all your men, who have just saved your life and the lives of your sons and daughters and the lives of your wives and concubines. 6You love those who hate you and hate those who love you. You have made it clear today that the commanders and their men mean nothing to you. I see that you would be pleased if Absalom were alive today and all of us were dead. 7Now go out and encourage your men. I swear by the Lord that if you don’t go out, not a man will be left with you by nightfall. This will be worse for you than all the calamities that have come on you from your youth till now.”
At least some commentators have suggested that this may have been an implied threat. For example, in his study Bible's notes on verse 7, Dr. John MacArthur argues:
Joab, who was the esteemed general of the army, was a dangerous person because of that power. He was also dangerous to David because he had disobeyed his command to spare Absalom, and killed him with no remorse. When he warned David that he would be in deep trouble if he did not immediately express appreciation to his men for their victory, David knew he could be in serious danger.
This seems to suggest that Joab himself could've been dangerous to David if he didn't comply (i.e. that he was making a threat, not just a prediction, here). The fact that Joab prefaces his statement with "I swear by the Lord..." could also suggest that he was making a threat rather than just a prediction.
Which was this - a threat or a prediction? If it was a threat, what exactly was the threat (i.e. what might Joab have done)? What are textual arguments either way?