From the early Church Fathers to now.
“Because you offended me in the desert of Sin in the contradiction of the multitude, neither would you sanctify me before them at the waters. These are the waters of contradiction in Cades of the desert of Sin.”
“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?”
“But when the land of promise had at length been reached, [Moses] was called into the mountain and heard of the fault which he had committed eight and thirty years before, as I have said, in that he had doubted about drawing water from the rock. And for this reason he was told that he might not enter the land of promise. Herein it is for us to consider how formidable is the judgment of the almighty God, who did so many signs through that servant of his whose fault he still bore in remembrance for so long a time.”
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.