Commentary on the Bible, by Adam Clarke, [1831], at sacred-texts.com
David is tempted by Satan to take the numbers of the people of Israel and Judah, Ch1 21:1, Ch1 21:2. Joab remonstrates, but the king is determined, and Joab pleads in vain, Ch1 21:3, Ch1 21:4. He returns, and delivers in the number to the king, but reckons not Levi and Benjamin, Ch1 21:5. The Lord is displeased, and sends Gad to offer David his choice of three great national calamities; famine, war, or pestilence, Ch1 21:6-12. David submits himself to God, and a pestilence is sent, which destroys seventy thousand, Ch1 21:13, Ch1 21:14. At David's intercession the destroying angel is restrained at the threshing-floor of Ornan, Ch1 21:15-17. He buys the piece of ground, builds an altar to the Lord and offers sacrifices, and the plague is stayed, Ch1 21:18-30.
And Satan stood up against Israel - See the notes on the parallel place, Sa2 24:1 (note), etc.
All they of Israel were a thousand thousand - Judah was four hundred threescore and ten thousand - In the parallel place, Sa2 24:9 (note), the men of Israel are reckoned eight hundred thousand, and the men of Judah five hundred thousand.
Levi and Benjamin counted he not - The rabbins give the following reason for this: Joab, seeing that this would bring down destruction upon the people, purposed to save two tribes. Should David ask, Why have you not numbered the Levites? Joab purposed to say, Because the Levites are not reckoned among the children of Israel. Should he ask, Why have you not numbered Benjamin? he would answer, Benjamin has been already sufficiently punished, on account of the treatment of the woman at Gibeah: if, therefore, this tribe were to be again punished, who would remain?
Three days - the pestilence in the land - In Sa2 24:13 (note), seven years of famine are mentioned.
David said - I am in a great strait - The Targum reasons thus:
"And David said to Gad, If I choose famine, the Israelites may say, The granaries of David are full of corn; neither doth he care should the people of Israel die with hunger. And if I choose war, and fly before an enemy, the Israelites may say, David is a strong and warlike man, and he cares not though the people of Israel should fall by the sword. I am brought into a great strait; I will deliver myself now into the Hand of the Word of the Lord, ביד מימרא דיי beyad meymera dayai, for his mercies are many; but into the hands of the children of men I will not deliver myself."
And God sent an angel - Thus the Targum: "And the Word of the Lord sent the angel of death against Jerusalem to destroy it; and he beheld the ashes of the binding of Isaac at the foot of the altar, and he remembered his covenant with Abraham, which he made in the Mount of Worship; and the house of the upper sanctuary, where are the souls of the righteous, and the image of Jacob fixed on the throne of glory; and he turned in his Word from the evil which he designed to do unto them; and he said to the destroying angel, Cease; take Abishai their chief from among them, and cease from smiting the rest of the people. And the angel which was sent from the presence of the Lord stood at the threshing-floor of Araunah the Jebusite.
Ornan turned back, and saw the angel - The Septuagint say, And Orna turned, και ειδε τον βασιλεα, and saw the King. The Syriac and Arabic say, David saw the angel; and do not mention Ornan in this place. Houbigant translates the same reading המלך hammalech, the king, for המלעך hammalach, the angel, and vindicates his version from the parallel place, Sa2 24:20, where it is said, he saw David: but there is no word of his seeing the angel. But the seeing David is mentioned in Ch1 21:21; though Houbigant supposes that the 20th verse refers to his seeing the king while he was at a distance; the 21st, to his seeing him when he came into the threshing-floor. In the first instance he and his sons were afraid when they saw the king coming, and this caused them to hide themselves; but when he came into the threshing-floor, they were obliged to appear before him. One of Kennicott's MSS. has המלך the king, instead of המלאך the angel. Some learned men contend for the former reading.
For the full price - That is, six hundred shekels full weight of pure gold.
He answered him - by fire - In answer to David's prayers, God, to show that he had accepted him, and was now pacified towards him and the people, sent fire from heaven and consumed the offerings.
Because of the sword of the angel - This is given as a reason why David built an altar in the threshing-floor of Ornan: he was afraid to go to Gibeon, because of the sword of the destroying angel, or he was afraid of delaying the offerings so long as his going thither would require, lest the destroying angel should in the mean while exterminate the people; therefore he hastily built an altar in that place, and on it made the requisite offerings, and by the fire from heaven God showed that he had accepted his act and his devotion. Such interventions as these must necessarily maintain in the minds of the people a full persuasion of the truth and Divine origin of their religion.
For a more circumstantial account of these transactions, see the notes on Sa2 24:1, Ac., in which several difficulties of the text are removed.