God considered Moses's disobedience as rebellious as that of Israel when he spoke to Israel and struck the rock twice.
Num 20:8 "Take the rod; and you and your brother Aaron assemble the congregation and speak to the rock before their eyes, that it may yield its water. You shall thus bring forth water for them out of the rock and let the congregation and their beasts drink."
Num 20:12 But the LORD said to Moses and Aaron, "Because you have not believed Me, to treat Me as holy in the sight of the sons of Israel, therefore you shall not bring this assembly into the land which I have given them."
God considered it irreverent when Uzzah touched the Ark of the Covenant as it was about to fall to the ground. God had already commanded how the Ark should be handled, yet the Israelites were pragmatic by using a "new" pagan cart to carry the holy item.
2Sa 6:6 But when they came to the threshing floor of Nacon, Uzzah reached out toward the ark of God and took hold of it, for the oxen nearly upset it. 7 And the anger of the LORD burned against Uzzah, and God struck him down there for his irreverence; and he died there by the ark of God.
Nadab and Abihu offered strange fire to worship or honor the LORD but that wasn't what God required, nor was it good enough because its source was not from God:
Lev 10:1 Now Nadab and Abihu, the sons of Aaron, took their respective firepans, and after putting fire in them, placed incense on it and offered strange fire before the LORD, which He had not commanded them. 2 And fire came out from the presence of the LORD and consumed them, and they died before the LORD.