*Minor differences ignored. Grouped by changes, with first version listed as example.
Again - It should be, "and David again gathered," etc., i. e. after the previous gathering, either for his election to the kingdom 2-Samuel 5:1-3 or for the Philistine war 2-Samuel 5:17-25, he assembled them again for the peaceful purpose of bringing up the ark to Mount Zion (see marginal reference). The whole narrative indicates the progressive consolidation of David's power, and the settlement of his monarchy on strong foundations.
Thirty thousand - This is supposed to have been a new levy; and thus he augmented his army by 30,000 fresh troops. The Septuagint has 70,000.
Again, David gathered together all the chosen men of Israel, thirty thousand. Which was done by the advice of his officers, 1-Chronicles 13:1; the word "again" refers either to the gathering of them when they made him king in Hebron, as the Jewish writers generally observe; but then they gathered themselves, and not David: or rather to his gathering them to fight the Philistines a little while ago; and as they were the choice and young men that were gathered for war, as being the fittest, so now to fetch up the ark with dancing and singing, and to protect it; the Septuagint version says they were about seventy thousand; but the Targum, Syriac, and Arabic versions, have thirty thousand, agreeably to the Hebrew text.
God is present with the souls of his people, when they want the outward tokens of his presence; but now David is settled in the throne, the honour of the ark begins to revive. Let us learn hence, to think and to speak highly of God; and to think and speak honourably of holy ordinances, which are to us as the ark was unto Israel, the tokens of God's presence, Matthew 28:20. Christ is our Ark; in and by him God manifests his favour, and accepts our prayers and praises. The ark especially typified Christ and his mediation, in which the name of Jehovah and all his glories are displayed. The priests should have carried the ark upon their shoulders. Philistines may carry the ark in a cart without suffering for it; but if Israelites do so, it is at their peril, because this was not what God appointed.
DAVID FETCHES THE ARK FROM KIRJATH-JEARIM ON A NEW CART. (2-Samuel 6:1-5)
Again, David gathered together all the chosen men of Israel--(See 2-Samuel 5:1). The object of this second assembly was to commence a national movement for establishing the ark in Jerusalem, after it had continued nearly fifty years in the house of Abinadab (see on 1-Chronicles 13:1).
The ark fetched from Kirjath-jearim. - 2-Samuel 6:1. "David assembled together again all the chosen men in Israel, thirty thousand." יסף for יאסף is the Kal of אסף, as in 1-Samuel 15:6; Psalm 104:29. עוד, again, once more, points back to 2-Samuel 5:1, 2-Samuel 5:3, where all Israel is said to have assembled for the first time in Hebron to anoint David king. It is true that that assembly was not convened directly by David himself; but this was not the point in question, but merely their assembling a second time (see Bertheau on 1-Chronicles 13:5). בּחוּר does not mean "the young men" here (νεάνια, lxx), or "the fighting men," but, according to the etymology of the word, "the picked men." Instead of thirty thousand, the lxx have seventy chiliads, probably with an intentional exaggeration, because the number of men in Israel who were capable of bearing arms amounted to more than thirty thousand. The whole nation, through a very considerable body of representatives, was to take part in the removal of the ark. The writer of the Chronicles gives a more elaborate account of the preparations for these festivities (1-Chronicles 13:1-5); namely, that David took counsel with the heads of thousands and hundreds, and all the leaders, i.e., all the heads of families and households, and then with their consent collected together the whole nation from the brook of Egypt to Hamath, of course not every individual, but a large number of heads of households as representatives of the whole. This account in the Chronicles is not an expansion of the brief notice given here; but the account before us is a condensation of the fuller description given in the sources that were employed by both authors.
*More commentary available at chapter level.