For the saw as an implement of torture compare Hebrews 11:37.
Harrows of iron - Or rather thrashing-machines (Isaiah 28:27; Isaiah 41:15, etc.).
Axes - The word so rendered occurs only here and in 1 Chronicles 20:3. It evidently means some cutting instrument.
Made them pass through the brick-kiln - The phrase is that always used of the cruel process of making their children pass through the fire to Moloch, and it is likely that David punished this idolatrous practice by inflicting something similar upon the worshippers of Moloch. The cruelty of these executions belongs to the barbarous manners of the age, and was provoked by the conduct of the Ammonites 2 Samuel 10:1-4; 1 Samuel 11:1-2, but is utterly indefensible under the light of the Gospel. If Rabbah was taken before David’s penitence, he may have been in an unusually harsh and severe frame of mind. The unpleasant recollection of Uriah’s death would be likely to sour and irritate him to the utmost.