Complete Commentary on the Whole Bible, by Matthew Henry, , at sacred-texts.com
Here is a repetition of the story of David's wars, I. With the Ammonites, and the taking of Rabbah (Ch1 20:1-3). II. With the giants of the Philistines (Ch1 20:4-8).
1 Chronicles 20:1
How the army of the Ammonites and their allies was routed in the field we read in the foregoing chapters. Here we have the destruction of Rabbah, the metropolis of their kingdom (Ch1 20:1), the putting of their king's crown upon David's head (Ch1 20:2), and the great severity that was used towards the people, Ch1 20:3. Of this we had a more full account in 2 Sa. 11, 12, and cannot but remember it by this sad token, that while Joab was besieging Rabbah David fell into that great sin in the matter of Uriah. But it is observable that, though the rest of the story is repeated, that is not: a hint only is given of it, in those words which lie here in a parenthesis - But David tarried at Jerusalem. If he had been abroad with his army, he would have been out of the way of that temptation; but, indulging his ease, he fell into uncleanness. Now, as the relating of the sin David fell into is an instance of the impartiality and fidelity of the sacred writers, so the avoiding of the repetition of it here, when there was a fair occasion given to speak of it again, is designed to teach us that, though there may be a just occasion to speak of the faults and miscarriages of others, yet we should not take delight in the repetition of them. That should always be looked upon as an unpleasing subject which, though sometimes one cannot help falling upon, yet one would not choose to dwell upon, any more than we should love to rake in a dunghill. The persons, or actions, we can say no good of, we had best say nothing of.
1 Chronicles 20:4
The Philistines were nearly subdued (Ch1 18:1); but, as in the destruction of the Canaanites by Joshua the sons of Anak were last subdued (Jos 11:21), so here in the conquest of the Philistines the giants of Gath were last brought down. In the conflicts between grace and corruption there are some sins which, like these giants, keep their ground a great while and are not mastered without much difficulty and a long struggle: but judgment will be brought forth unto victory at last. Observe, 1. We never read of giants among the Israelites as we do of the giants among the Philistines - giants of Gath, but not giants of Jerusalem. The growth of God's plants is in usefulness, not in bulk. Those who covet to have cubits added to their stature do not consider that it will but make then more unwieldy. In the balance of the sanctuary David far outweighs Goliath. 2. The servants of David, though men of ordinary stature, were too hard for the giants of Gath in every encounter, because they had God on their side, who takes pleasure in abasing lofty looks, and mortifying the giants that are in the earth, as he did of old by the deluge, though they were men of renown. Never let the church's friends be disheartened by the power and pride of the church's enemies. We need not fear great men against us while we have the great God for us. What will a finger more on each hand do, or a toe more on each foot, in contest with Omnipotence? 3. These giants defied Israel (Ch1 20:7) and were thus made to pay for their insolence. None are more visibly marked for ruin that those who reproach God and his Israel. God will do great things rather than suffer the enemy to behave themselves proudly, Deu 32:27. The victories of the Son of David, like those of David himself, are gradual. We see not yet all things put under him; but it will be seen shortly: and death itself, the last enemy, like these giants, will be triumphed over.