For the cities of our God - This rather indicates that the relief of Medeba was one of the immediate objects in view, and consequently that at this time Medeba was still in the possession of the Reubenites. To prevent an Israelite city falling into the hands of a pagan people, and the rites of Moloch being substituted for the worship of Yahweh, was a very urgent motive to valor.

Be of good courage - This is a very fine military address, and is equal to any thing in ancient or modern times. Ye fight pro aris et focis; for every good, sacred and civil; for God, for your families, and for your country.

Be of good courage, and let us play the men for (e) our people, and for the cities of our God: and the LORD do that which seemeth him good.
(e) Here it is declared why war should be undertaken: for the defence of true religion and God's people.

Be of good courage, and let us play the men,.... This Joab said, not only to encourage Abishai and himself, but in the hearing of the rest of the officers of the army, and of many of the people, to hearten them to the battle; who might be somewhat intimidated with the number of their enemies, and the position they were in, being before and behind them; and therefore he thought proper to make such a speech to them to animate them to light:
for our people, and for the cities of our God; that the people of Israel might not be carried captive, and their cities spoiled and plundered; and instead of being cities where the people of God dwelt, and he was worshipped, would, if taken, become the habitations of idolatrous Heathens, and where temples would be erected to idols, and the worship of them; these were the arguments he used to engage them to fight manfully for their country, the liberties and religion of it:
and the Lord do that which seemeth him good: tacitly suggesting that victory was of the Lord, and that it became them to do their part in fighting courageously, and leave the issue to the Lord, on whom alone success depended.

"Be firm, and let us be firm (strong) for our people, and for the towns of our God: and Jehovah will do what seemeth Him good." Joab calls the towns of Israel the towns of our God, inasmuch as the God of Israel had given the land to the people of Israel, as being His own property. Joab and Abishai were about to fight, in order that Jehovah's possessions might not fall into the hands of the heathen, and become subject to their gods.