How did the entire congregation manage to stand in front of the rock?
Why did they call the people "ha'Morim"?
Rashi: The word means both rebels (or people who refuse to listen or fools) and teachers, who instruct their teachers. 1
Ramban (citing Rambam in Moreh Nevuchim): It means 'rebels', and this was Moshe's sin - displaying anger. 2
Rashbam: He pointed to Aharon's stick with its almonds.
Why did Moshe insert the word "Na"?
Targum Onkelos and Targum Yonasan: "Na" here means (not 'please' but) 'now'. 1
What did Moshe mean when he said "ha'Min ha'Sela ha'Zeh Notzi lachem Mayim"? What made them ask such a question?
Rashi: When the well ceased to function, the rock that contained it went and placed itself among the other rocks in the vicinity; and when Moshe and Aharon failed to recognize it, the people impatiently asked him what difference it would make from which rock they would produce water. That is when he said in reply 'How can we produce water from a rock that Hashem did not command us?' 1
Ramban #1 (citing the R'dak): It is a rhetoric, 2 implying that they would indeed produce water from the rock.
Ramban #2 (citing Ibn Ezra): They meant to ask 3 how they (Moshe and Aharon) were able to produce water, implying that only Hashem was capable of doing that 4 - and that He was the One who took them out of Egypt, He was the One who brought them to 'this bad place' and who would sustain them there.
Ramban #3: He was asking them what they thought about Hakadosh-Baruch-Hu; whether He would produce water from the rock or not. 5
Ramban (on Pasuk 8, citing R. Chananel): This was Moshe and Aharon's sin, in that they said 'Notzi' instead of 'Yotzi', (inadvertently) attributing the miracle to themselves 6 rather than to Hashem. 7 And not seeing a sign that Hashem was there, 8 some people believed that it was Moshe and Aharon who prodyuced water from the rock.
Rashbam: He said it in anger, as he raised his hand and struck the rock twice, doubting that it would produce water. 9
See Ramban, who maintains that it is inconceivable to suggest that Moshe erred in a prophecy.
Ramban: In reply to the people's having blamed him for bringing them to such a bad place. Refer to 20:3:1:1.
And that He was about to do so now!
Ramban: The 'or not' is self-understood, because he was asking whether they didn't believe that Hashem could do it, as we find in other places - See for example, Bereishis 24:5 and Divrei Hayamim 2, 18:5. In fact, after calling them rebels, he was now accusing them of being Ketanei Emunah - because it was obvious that Hashem could produce water from the rock - just as David ha'Melech said in Tehilim, 78:18-20 in connection with this very same incident.
Ramban: Which explains why the Torah writes in Devarim 32:51 "Ya'an Lo Kidashtem Osi" and "Me'altem Bi" (See Ramban, DH 've'ha'Karov min ha'Devarim').