Why did Moshe hit the rock twice rather than once in Bamidbar 20:11?
The Beer Mayim Chaim Answers:
If you take the word סלע and write it with all it letters spelled out (this is a Kabbalistic system) out you get.
Now ,we can understand why it says וְדִבַּרְתֶּם אֶל הַסֶּלַע לְעֵינֵיהֶם וְנָתַן מֵימָיו Because in middle of the word סלע you have the word מים. This also explains why he had to hit it twice one to knock off the letter form each side of the words to get מים.
Rashi on the verse (Bamidbar 20:11) says that Moshe had to hit it twice, since the first time only drops of water came out. Rashi then explains that drops only came out the first time since Moshe was not supposed to hit the rock, but rather talk to it.