Why did Moshe not know the Halachah?
Rashi #1: He forgot the Halachah because, after appointing judges in the time of Yisro, he said to them "Whatever is too difficult for you, bring to me ... " 1
Rashi #2 and Targum Yonasan #1: This Parshah was fit to have been said through Moshe, and it is because the B'nos Tz'lofchad were meritous that Hashem arranged for it to be said through them. 2
Targum Yonasan #2: Moshe actually knew the answer, and he claimed not to know it to teach the heads of Sanhedrin who would follow him not to be ashamed to say 'I don't know' and consult an authority higher than themselves. 3
Oznayim la'Torah and Chidushei ha'Rim: When Moshe heard that their father was not with Korach, rather, he wanted to Aharon to be Kohen Gadol, Moshe, afaird that he was slightly partial, declined to rule about this himself. Therefore, he brought the case before Hashem.
Rashi: See Devarim, 1:17. And this is considered boastful speech, even though he certainly said it without any feelings of pride. See also Oznayim la'Torah, DH 'va'Yakrev Moshe, #2, who elaborates on the answer.
Because if Moshe Rabeinu could say 'I don't know', how much more so they!
Why is the 'Nun' in "Mishpatan" big?
R. Bachye: It hints to a Chacham who is great in Torah. One should not decide a Torah law in front of someone greater than oneself. Rather, he brings the lawsuit in front of him.
Minchas Shai: It hints at the fifty ('Nun') gates of Binah (understanding), which Moshe merited - all but one (Nedarim 38a). 1
Sh'lah (Ta'anis, Torah Or 101): Yehoshua ben Nun brought Yisrael into Eretz Yisrael, whose air makes people wise, therefore he merited fiftygates of Binah. (I heard from R. Uziel Milevsky that the gate that Moshe lacked, pertained to Halachos of Eretz Yisrael - inheritance. Chizkuni - Moshe knew that daughters inherit when there are no sons. He did not know whether or not they inherit Ra'uy (property destined to come to their father) like Muchzak (what he owned when he died). Perhaps Moshe's doubt was only whether the inheritance of Eretz Yisrael, which was unique (refer to 26:55:3:1), was Ra'uy! - PF)
QUESTIONS ON RASHI
Rashi writes that Moshe forgot the Halachah because he told the judges "Whatever is too difficult for you, bring to me." Why did Rashi not give the same reason with regard to killing the Mekoshesh and the Megadef?
Perhaps this goes together with Rashi's second explantion - that the B'nos Tzelofchad merited that it should be said through them. (PF) 1
Some commentaries answer that, whereas regarding the Mekoshesh and the Megadef, Moshe could not possibly have known the answer, here he ought to have known, since it is logical that where there is no son, the daughter inherits.
Moshav Zekenim left this difficult; he understood that each answer suffices by itself. Or, also there, we could say that they 'merited 'that it be said through them. He could have asked why Rashi did not say so about Pesach Sheni. (PF)
