Charles Ellicott Commentary 2 Samuel 10:12

"Be of good courage, and let us play the man for our people, and for the cities of our God: and Jehovah do that which seemeth him good." — 2 Samuel 10:12 (ASV)

Be of good courage, and let us play the men. —Literally, Be strong and let us strengthen ourselves. The same phrase is translated in Chronicles, Be of good courage and let us behave ourselves valiantly. (Compare 1 Samuel 4:9.) Joab felt that the battle was a critical one, and on it depended the welfare and even the safety of our people and the cities of our God. The latter expression is in recognition of the fact that the whole land belonged to God, who allowed the use of it to His people.

The Lord do. —Rather, The Lord will do. Joab’s courage rose here to that highest point which is marked by the full trust that whatever may be the result, it will be that which seems best to Infinite wisdom and love.