In Numbers 27:13-14, the Lord announces to the leader of Israel, Moses, that his days are numbered. But the Lord in His infinite compassion allows Moses to go to the top of Mt. Nebo (biblical Pisgah) and see what he is missing, the land of promise.
The Lord then reminds the leader why he is prevented from entering the earthly Promised Land; because of his sin in the wilderness of Zin. What was his sin? The Lord tells the old man it was rebellion. What rebellion? you might ask.
It was when Moses struck the rock in anger caused by the people, when the Lord had only told him to speak to the rock. God said, Moses, you failed to "treat Me as holy before their eyes at the water." Those eyes were the eyes of the Hebrews who were watching him.
So rebellion, in God's eyes, is first, not taking His every word as a command and, second, not performing according to His word ... in this case in spite of the circumstances.
One more critical element is the nature of the rock Moses struck. Paul, in 1 Corinthians 10:1-4, tells us that this very rock was none other than the Messiah of Israel ... to Christians, the Christ - Jesus. That is not treating God "as holy" big time!