And Moses lifted up his hand, and with his rod he struck the rock twice: and the water came out abundantly, and the congregation drank, and their animals also.
All Commentaries on Numbers 20:11 Go To Numbers 20
Augustine of Hippo
AD 430
The rock is Christ in a sign, the true Christ in the Word and in the flesh. And how did they drink? The rock was struck twice with a rod. The double striking prefigures the two pieces of wood on the cross. .