Written by Benjamin A Rose
"...and he struck the rock with his staff, two times..." [Bamidbar, 20:11]
Rebbe Shaul Yedidya Elazar says we find that on the second day of Creation, Hashem did not use the words "ki tov", and it was good. Our Sages in the Midrash tell us that this was because the work of creating the waters (of earth), although begun, was not yet complete. Moshe Rabbeinu was suited to complete this work, as it says about him [Shemos, 2:10], "for I have drawn him out of the water." In addition, the words "ki tov" were used to describe Moshe [Shemos, 2:2]. Both of these occurred while Moshe was an infant. During the creation of the waters, the verse says, "And G-d said, 'Let there be a firmament in the midst of the waters, which should separate between water and water'...And G-d called the firmament "Shamayim" (Heaven)" [B'reishis, 1:6-8]
Rashi explains that the Heavens were actually created from a mixture of fire and water [aish u'mayim = Shamayim].
Moshe Rabbeinu sought to achieve the completion of the creation of the waters, in a similar vein - by combining fire and water. Just as Adam HaRishon discovered that fire could be formed by striking two stones together, Moshe wished to do the same. That is, since Hashem commanded him to draw water from the stone, Moshe wished to add "fire" to the equation, by striking the stone with his staff of stone, bringing out fire.
What then, was his mistake - where was his sin? Hashem wished to demonstrate the power of the tzaddikim. Just as in Creation, the Heavens were created with speech: as it says [Iyov, 26:11], "The pillars of the Heavens trembled, and stood in wonder at his scream." So it is that the tzaddik has the power, with speech alone, to create Heaven - fire and water - because "the tzaddik decrees and Hashem fulfills (his decree)" [Gemara Kesuvos, 103b].
It was for this very reason, says Reb Shaul, that the waters weren't completed in the first place - to demonstrate the creative powers of the earthly beings, by achieving a level of holiness. When our Sages say [Pirkei Avos, 5:1], that the Creation was made with ten utterances (instead of one) in order "to reward the tzaddikim who uphold the world that was created with ten utterances," Reb Shaul tells us that this indicates that the tzaddikim have the power of these ten utterances.
Finally, Reb Shaul explains the tefilla that we say in the blessings before the morning Shema in this light. We praise Hashem as the One Who, "in His Goodness, renews constantly, every day, the act of Creation." We then say, "ka'amur" (saying) - this refers to the speech of the tzaddikim. "He Who has formed the great lights" - another reference to the tzaddikim. "His Goodness is eternal," Amen
This is one of the reasons a person who really needs something is encouraged to go to a great tzaddik, either living to ask him for help or a grave [ohel] of a past Tzaddik to daven. If we daven with enough kavannah our prayers will be answered, because as the Gemara in Kesuvos says "the tzaddik decrees and Hashem fulfills (his decree)"