For the Shekhinah would rest upon the rock, for wherever the blessed Holy One wishes to perform a miracle, the Shekhinah precedes to that place, and since the Shekhinah was there, he Moses should not have struck the rock, because that was disrespectful to the Shekhinah, who was there, as though it did not have the power to give water, and this is: (Deut. 32:51)... because you did not sanctify Me... (Num. 20:12)... because you did not believe in Me to sanctify Me...
And because of this, the Shekhinah departed from the rock, which is the Yod י of Meytatron, and Metatron without Yod was left dry.