Why the outburst?

When King David first tried to move the Ark, an oxen stumbled nearly upsetting it, but when Uzzah reached out to steady the Ark, God struck him dead for his irreverence. Why?

The Ark was made with carrying poles and instructions not to remove them. When Moses finished setting up the tabernacle, the leaders of Israel gave an offering of covered carts and oxen.

The LORD instructed Moses to accept these things from them for use in the service of the tent of meeting, but Moses did not give any to the sons of Kohath because theirs was the service of the holy objects which they carried on the shoulder. This is summarized in 1 Chronicles 15:13-15 where it says,

“Because you did not carry it at the first, the LORD our God made an outburst on us, for we did not seek Him according to the ordinance.” So the priests and the Levites consecrated themselves to bring up the ark of the LORD God of Israel. The sons of the Levites carried the ark of God on their shoulders with the poles thereon, as Moses had commanded according to the word of the LORD.

References

2 Samuel 6:1-17 Moving the ark

1 Chronicles 13:1-14 Moving the ark

Exodus 25:13-15 Instructions for Ark

Numbers 7:2-9 no carts for Kohath

1 Chronicles 15:13-15 summary

Numbers 3:25-26 Duties of Gershon

Numbers 3:31 Duties of Kohath

Numbers 3:36-37 Duties of Merari

Psalm 105:37 not one stumbled

Hebrews 13:8 Jesus doesn’t change