Yet there had been an earlier occasion when God had told Moses to strike that very same rock: “Take in your hand your rod with which you smote the river. Strike the rock, and water shall come out of it, so that the people may drink” (Ex. 17:5-6).
If striking the rock was all right the first time, what was so wrong with it now?
A Midrashic answer is that God never performs the same miracle twice. Here the first miracle would occur by means of striking the rock, and the second by speaking to it.
We see how Divine miracles never repeat themselves in the fact that when Moses needed to sweeten bitter water he was told to cast a certain tree into it (Ex. 15:25), but when Elisha had to make water drinkable he was told to cast salt into it (II Kings 2:21).
In a sense we get the same message when the Siddur states that the Almighty “renews every day the work of Creation”. This does not necessarily indicate that God repeats the same creative miracle every day, but that every day is a new miracle. And since every day is new and miraculous, it offers human beings a wonderful fresh opportunity.
God does not go in for sameness, and neither should we.