Gregory the Great — on Num 27:14 (Register of Epistles Book 11, Epistle XXVIII)

“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.”