The Talmud’s description of the bond between Torah teacher and student is so strong that it alters our image of the relationship. A Torah teacher does not merely teach information or even a way of thinking. He remakes the student’s worldview, inspiring him and implanting within him a new personality. Such a relationship is transformational, akin to a rebirth.
It is no surprise, then, that when the Torah (Num. 3:1) announces the names of Moses’ and Aharon’s descendants but only lists Aharon’s, Rashi explains that Aharon’s sons were also Moshe’s. “Whoever teaches someone Torah is as if he fathered him.” As the primary Torah teacher of Aharon’s sons, Moshe was considered their father, as well.
However, as powerful as this comment may be, it seems like an understatement when compared with the Mishnah. On describing the obligation to return a lost object to its owner, the Mishnah (Bava Metzi’a 33a) states that of someone finds two lost objects, one belonging to his father and the other to his Torah teacher, the latter takes precedence. While his father brought the finder into this world, his religious mentor brings him into the next world. If so, why would Rashi say that a Torah teacher is life a father? A Torah teacher is greater than a parent!
I suggest that the answer lies in Prof. Gerald (Ya’akov) Blidstein’s explanation of this Mishnah. Prof. Blidstein (“Rabo Shel Adam Le-Umas Horav” in Iyunim Be-Machasheves Ha-Halakhah Ve-Ha-Aggadah, p. 88) explains that this is not a pragmatic comparison, that the Torah teacher to the spiritual which is greater than the physical world. Rather, the Torah teacher is also a father. And in choosing between fathers, you should choose the father who brings you into the greater world.
With this, we can understand Rashi’s comment about Moshe. A Torah teacher is a father. Like Aharon, Moshe was the father of the men listed. But he was their Torah mentor, the father who brought them into the next world as opposed to Aharon, the other father, who brought them into this world.