From the early Church Fathers to now.
“And when Moses had lifted up his hand, and struck the rock twice with the rod, there came forth water in great abundance, so that the people and their cattle drank,”
“Priests also must take care lest they be insincere, lest they doubt the power of God. If Aaron and Moses (who seemed to waver at the waters of contradiction) did not deserve to enter the Promised Land, does it not stand to reason that we, bent under the burden of sin, shall be far less able to cross the river Jordan and reach Gilgal, the place of circumcision, if we shall cause one of these little ones to sin?”
“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.”
“We recognize that we are taking a trip in a wasteland. If we recognize ourselves in a wasteland, we are in a wasteland. What does it mean, in a wasteland? In a desert. Why in a desert? Because in this world, one thirsts on a waterless road. But let us thirst that we may be filled. For "blessed are they who hunger and thirst for justice; for they shall have their fill." And our thirst is filled from a rock in the wasteland. For "the rock was Christ." And it was struck with a rod that water might flow. But that it might flow, it was struck twice; for there are the two pieces of wood on the cross.”
“"Therefore Moses struck the rock twice with his staff." What does this mean, brethren? I do not think it is without mystery. What does it mean that the rock was not struck once but twice with the staff? The rock was struck a second time because two trees were lifted up for the gibbet of the cross: the one stretched out Christ's sacred hands, the other spread out his sinless body from head to foot.”
The in-app commentary runs from the Fathers to the early-modern record, then stops — that's where the public-domain sources end, not where the reading does. For the modern reading, follow the sources directly.