Charles Spurgeon Commentary 1 Chronicles 13:9-10

"And when they came unto the threshing-floor of Chidon, Uzza put forth his hand to hold the ark; for the oxen stumbled. And the anger of Jehovah was kindled against Uzza, and he smote him, because he put forth his hand to the ark; and there he died before God." — 1 Chronicles 13:9-10 (ASV)

I suppose that Uzza, because the ark had been in his father's house for so long, had grown unduly familiar with it and therefore touched it. Yet it was an express law that even the Levites should not lay a hand upon the ark. They carried it with staves; the priests alone might touch it for necessary purposes. It was for this profanation that Uzza died before God.