The meaning is, not that they sacrificed oxen and fatlings every six steps, which would have been impossible, but that when - after the arrangement made by David for the Levites to carry the ark 1-Chronicles 15:2, 1-Chronicles 15:12, 1-Chronicles 15:15 they had borne it successfully and with visible tokens of God's favor, out of the house of Obed-edom and six "steps" on the road to the city of David to the sound of the musical instruments - then they stopped and offered solemn sacrifices. Possibly "the step" may have had a technical sense, and denoted a certain distance, say a stadium. Six such distances would have been nearly a mile, and if the ground was difficult and steep, the successful progress of "those that bare the ark," so far, would have been a fit cause for a thanksgiving sacrifice.

And it was so, that when they that bare the ark of the Lord,.... The Levites; for now David had seen the former mistake, and rectified it, and ordered the Levites to "carry" it, as they did upon their shoulders, with the staves therein, see 1-Chronicles 15:2; when these
had gone six paces, he sacrificed oxen and fatlings; upon an altar, which was at once erected for that purpose; the number and kind of sacrifices offered were seven bullocks and seven rams, 1-Chronicles 15:26; and these David offered, not by himself, but by the priests that were with him, and that as soon as they had gone six paces from the house of Obededom; whereby they perceived the Levites, were able to carry the ark, with what was in it, the Lord helping them, as in 1-Chronicles 15:2, and without stumbling and falling, or any evil attending them; and Kimchi thinks these six paces were just the measure of the ground Uzzah went before what befell him; but it is highly probable that he had gone further; however, no doubt by the order of David, the Levites set down the ark, and sacrifices were offered by way of thanksgiving to God, and for the continuance of his goodness, and for atonement for former errors. Some think these seven oxen and rams were offered, at seven different times and places, at every six paces an ox and a ram; but this is not very likely.

when they that bare the ark . . . had gone six paces--Some think that four altars were hastily raised for the offering of sacrifices at the distance of every six paces (but see on 1-Chronicles 15:26).

The bearers of the ark are not particularly mentioned in this account; but it is very evident that they were Levites, as the Chronicles affirm, from the fact that the ark was carried this time, and not driven, as before. "And it came to pass, when the bearers of the ark of Jehovah had gone six paces, he sacrificed an ox and a fatted calf" (i.e., had them sacrificed). These words are generally understood as meaning, that sacrifices of this kind were offered along the whole way, at the distance of six paces apart. This would certainly have been a possible thing, and there would be no necessity to assume that the procession halted every six paces, until the sacrificial ceremony was completed, but the ark might have continued in progress, whilst sacrifices were being offered at the distances mentioned. And even the immense number of sacrificial animals that would have been required is no valid objection to such an assumption. We do not know what the distance really was: all that we know is, that it was not so much as ten miles, as Kirjath-jearim was only about twelve miles from Jerusalem, so that a few thousand oxen, and the same number of fatted calves, would have been quite sufficient. But the words of the text do not distinctly affirm that sacrifices were offered whenever the bearers advanced six paces, but only that this was done was soon as the bearers had taken the first six steps. So that, strictly speaking, all that is stated is, that when the procession had started and gone six paces, the sacrifice was offered, namely, for the purpose of inaugurating or consecrating the solemn procession. In 1 Chron 15 this fact is omitted; and it is stated instead (1-Chronicles 15:26), that "when God helped the Levites that bare the ark of the covenant of the Lord, they offered seven bullocks and seven rams," i.e., at the close of the procession, when the journey was ended, to praise God for the fact that the Levites had been enabled to carry the ark of God to the place appointed for it, without suffering the slightest harm.
(Note: There is no discrepancy, therefore, between the two different accounts; but the one supplements the other in a manner perfectly in harmony with the whole affair, - at the outset, a sacrifice consisting of one ox and one fatted calf; and at the close, one of seven oxen and seven rams. Consequently there is no reason for altering the text of the verse before us, as Thenius proposes, according to the senseless rendering of the lxx, καὶ ἦσαν μετ ̓ αὐτοῦ αἴροντες τὴν κιβωτὸν ἑπτὰ χοροί, καὶ θῦμα μόσχος καὶ ἄρνες ("with David there were bearers of the ark, seven choirs, and sacrifices of a calf and lambs"), which has also found its way into the Vulgate, though Jerome has rendered our Hebrew text faithfully afterwards (i.e., after the gloss, which was probably taken from the Itala, and inserted in his translation).)