In the passage Samuel 6:6-6:7 is says “When they came to the threshing floor of Nakon, Uzzah reached out and took hold of the ark of God, because the oxen stumbled. The Lord’s anger burned against Uzzah because of his irreverent act;therefore God struck him down, and he died there beside the ark of God.” https://www.biblegateway.com/passage/?search=2%20Samuel%206-7

I didn’t understand why God would kill someone who touched the Ark just because the Oxen stumbled. This website has the following statement after explaining further 

https://www.rationalchristianity.net/touch_ark.html

The Israelites who looked in the ark were actually violating several laws: they came near to the ark (a violation if they weren’t Levites), they looked at the ark, they touched the ark and they moved the atonement cover, which was God’s symbolic throne. Since God’s presence was on/over the ark, they were actually coming into the presence of God – and without the least sense of reverence towards him, since they decided to poke around and play with his throne! Is it any wonder they died?”

This website has a little more clarity around it and does a great job of explaining why http://christianapologeticsalliance.com/2015/03/25/why-did-god-kill-uzzah-for-trying-to-protect-the-ark-of-covenant/

“Never would a king be tossed in the back of an oxen cart because the servants didn’t feel like carrying him. Royalty were to be treated with the utmost respect. And while Israel’s enemies did not realize the significance of the Ark of the Covenant as God’s presence when they returned it on an oxen cart, the Israelites did.”