“In the 6th chapter of 2 Samuel we read of the disastrous attempt by David to bring back the ark of the covenant to Israel. The ark is introduced in verse 2 as ‘the ark of God, whose name is called by the Name the LORD of hosts who dwells between the cherubim.’ The emphasis here is upon the holy nature of the ark as the representation of God's holy presence among His people. Sadly, in disregard of God's holiness, David and his men placed the ark on a cart drawn by oxen, and two men were appointed to drive the team along the bumpy roads. When the oxen stumbled, one of these men, Uzzah, reached out his hand to steady the ark. The result was immediate death from the wrath of God…
… James Glasgow wrote ‘David proceeded irregularly, because he was without scriptural authority. Thus, instead of consulting the priests and Levites to whose custody the ark belonged, he ‘consulted with the captains of thousands and hundreds, and every leader,’ (according to 1 Chronicles 13:1), that is, with political and military advisers… The result in David's case implies a permanent inhibition of introducing any religious observance without divine authority. If David could not do this, how can it, without sinful responsibility, be done by men in the 19th century? Instead of allowing the ark to be borne by the Levites, he had it placed on a cart-which he doubtlessly thought was done ‘decently and in order.’ This, however, was not appointed and therefore he erred in doing it.’
Michael Bushell gets to the root of the matter when he writes ‘The heart of Uzzah’s transgression lies in the fact that according to Numbers 4, the ark was… ‘to be moved only by means of the staves on the side of the ark, on the shoulders of the Levites, and not on a cart.
Instead of following these instructions, they followed the example of the Philistines who sometime earlier had sent the ark back by cart. The Lord's command as to how the ark was to be moved excluded every other means. What was not commanded was forbidden, however much the circumstances may have suggested otherwise.’
The dramatic death of Uzzah underscores the fact that God is in earnest regarding the conformity of His people to His commandments, when they draw near to Him in worship. That David recognized this is clear from his instruction to the Levites recorded in 1 Chronicles 15: 12-13, when the ark was later successfully transported to Israel: ‘sanctify yourselves, you and your brethren, that you may bring up the ark of the Lord God of Israel to the place I have prepared for it. For because you did not do it the first time, the Lord our God broke out against us, because we did not consult Him about the proper order.’”
(Comin 89-90)