John Gill's Bible Commentary Ver. 4. Then said the king to Amasa , etc.] 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.
Matthew Henry Commentary
Verses 4-13 - Joab barbarously murdered Amasa. The more plot there is in a sin, the worse it is. Joab contentedly sacrificed the interest both of the kin 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.
Original Hebrew ויאמר559 המלך4428 אל413 עמשׂא6021 הזעק2199 לי את853 אישׁ376 יהודה3063 שׁלשׁת7969 ימים3117 ואתה859 פה6311 עמד׃5975