4 Then the king said to Amasa, "Call me the men of Judah together within three days, and be here present."
*Minor differences ignored. Grouped by changes, with first version listed as example.
To Amasa - Evidently feeling his way toward fulfilling the promise to Amasa (marginal reference).
Then said the king to Amasa - Thus he invests him with the command of the army, and sends him to collect the men of Judah, and to come back to receive his orders in relation to Sheba, in three days. It appears that Amasa found more difficulty in collecting his country-men than was at first supposed; and this detaining him beyond the three days, David, fearing that Sheba's rebellion would get head, sent Abishai, who it appears was accompanied by Joab, to pursue after Sheba.
Amasa, it seems, got up with them at Gibeon, 2-Samuel 20:8, where he was treacherously murdered by the execrable Joab.
Then said the king to (e) Amasa, Assemble me the men of Judah within three days, and be thou here present.
(e) Who was his chief captain in Joab's place, (2-Samuel 19:13).
Then said the king to Amasa,.... Whom he had promised to make general of his army, 2-Samuel 19:13; and by the following order declared him such:
assemble me the men of Judah within three days; which was done by the sound of the trumpet, or by the proclamation of a herald; it seems that the men of Judah, who attended David to Jerusalem, were gone to their respective cities and places of abode, or there would have been no occasion for such a summons; though it is strange they should, when the men of Israel appeared so inclinable to a new rebellion:
and be thou here present; to take the command of them.
Joab barbarously murdered Amasa. The more plot there is in a sin, the worse it is. Joab contentedly sacrificed the interest both of the king and the kingdom to his personal revenge. But one would wonder with what face a murderer could pursue a traitor; and how, under such a load of guilt, he had courage to enter upon danger: his conscience was seared.
Then said the king to Amasa, Assemble me the men of Judah within three days--Amasa is now installed in the command which David had promised him. The revolt of the ten tribes, probably, hastened the public declaration of this appointment, which he hoped would be popular with them, and Amasa was ordered within three days to levy a force from Judah sufficient to put down the insurrection. The appointment was a blunder, and the king soon perceived his error. The specified time passed, but Amasa could not muster the men. Dreading the loss of time, the king gave the commission to Abishai, and not to Joab--a new affront, which, no doubt, wounded the pride of the stern and haughty old general. But he hastened with his attached soldiers to go as second to his brother, determined to take the first opportunity of wreaking his vengeance on his successful rival.
David then ordered Amasa to call the men of Judah to pursue Sheba the rebel, and attack him within three days, and then to present himself to him again. This commission was intended as the commencement of the fulfilment of the promise which David had given to Amasa (2-Samuel 19:14). It was no doubt his intention to give him the command over the army that marched against Sheba, and after the defeat of the rebel to make him commander-in-chief. But this first step towards the fulfilment of the promise was a very imprudent act, like the promise itself, since Joab, who had been commander of the army for so many years, was grievously offended by it; and moreover, being a well-tried general, he had incomparably more distinction in the tribe of Judah than Amasa, who had taken part in Absalom's rebellion and even led the rebel army, could possibly have.
*More commentary available at chapter level.