The greatness of the student. The greatness of the father
ואלה תולדת אהרן ומשה ביום דבר יקוק את-משה בהר סיני: ואלה שמות בני-אהרן וגו’
These are the offspring of Aharon and Moshe, on the day that Hashem spoke to Moshe on Mount Sinai. These are the names of the children of Aharon…
The book of Bamidbar earns its English title of “Numbers” by beginning with several numbers. Namely, it details two different censuses that were taken before the Jews departed from Mount Sinai. The Torah introduces the census of the tribe of Levi by listing for us the offspring of Moshe and Aharon. The problem is, the Torah only lists the children of Aharon. What about the children of Moshe? This anomaly prompts our Sages to tell us that we learn from here that one who teaches his friend’s children Torah is looked at as if they had birthed them. Meaning, Moshe taught Aharon’s children Torah, and they are therefore, in a sense, considered Moshe’s children.
The thing is, this explanation is insufficient. What does it mean that they’re considered as if they had birthed them? In what way? Who cares? What difference does it make? One would think that teaching a friend’s children Torah is itself a lofty cause in and of itself, with immeasurable reward. The reward should make any “consideration” insignificant in comparison.
One could suggest that this statement is to teach us the praise of Nadav and Avihu, two of Aharon’s sons who died tragically. There’s a concept known as bara mezakeh abbah, that a son can provide merit for a father. For example, although once we part from this world we are no longer able to accrue merit, our children can do so on our behalf. They can do this by reciting kaddish, performing mitzvos, and the like. While this usually applies to one’s biological offspring, perhaps we can say this is the intent of the teaching of our Sages. Someone who teaches a friend’s children is considered as if they birthed them, to the point that even they can provide merit for the teacher.
Now, this teaching should have interesting ramifications. Moshe taught the Torah to the entire Jewish people. Is he considered then the father of all of them? Seemingly not. The reason is because Moshe had no need for their merit, for who is greater than Moshe? However, our Sages tell us that Nadav and Avihu were, in a sense, on a greater level than even Moshe. It would make sense then for the Torah to tell us that the offspring of Aharon were like the offspring of Moshe. It’s to teach us that Nadav and Avihu, on their great level, were even able to provide some merit for Moshe, their teacher.
We can also now clarify a comment of Rashi on the end of the verse. The Torah stresses “on the day that Hashem spoke to Moshe on Mount Sinai”. Rashi tells us that this is referring to when the children of Aharon “became” the children of Moshe. What does he mean? It’s based on the fact that, as we said, in some ways Nadav and Avihu were greater than Moshe.
Despite their greatness, we know that Hashem only spoke “face to face” with Moshe. Why is that? It’s due to his humility. In terms of humility, Nadav and Avihu were the opposite of Moshe. Our Sages tell us that one of their sins was that they didn’t’ get married, for they didn’t feel anyone was a suitable match for their stature. Our Sages also tell us that the reason that the Torah was given on Mount Sinai, of all mountains, because it was the lowest of them all. This was meant to represent humility, the appropriate trait for acquiring Torah.
All this is alluded to in the verse we started with. Nadav and Avihu “became” the offspring of Moshe, since he taught them Torah, on the day that Hashem spoke to Moshe on Mount Sinai. Meaning, in terms of humility, their lower stature than Moshe became evident when Hashem spoke exclusively to Moshe, on the lowest of Mountains, due to his humility. That’s something they were lacking, and in this sense Moshe was their father. They were considered his offspring both because they had much more to learn from their teacher, and because they were able to provide merit for him.
 Based on Chasm Sofer’s Toras Moshe I to Numbers 3:1
 Numbers 3:1,2
 Sanhedrin 19b, brought by Rashi ad. loc.
 Sanhedrin 104a
 This innovation of the Chasam Sofer is consistent with his comments in Chasam Sofer al HaTorah parshas Beha’alosecha s.v. ונתתי לך מהלכים and to Deuteronomy 31:16 s.v. בפ’ חלק
 Toras Kohanim and Midrash Aggadah to Leviticus 10:3; Vayikra Rabbah 12:2; Midrash Tanchuma Shemini § 1; Zohar III parshas Acharei Mos p. 56b
 Numbers 12:8
 Vayikra Rabbah 20:10. See Psalms 78:63
 Sotah 5a