While discussing whether the primary family relationship regarding laws of inheritance is from the mother’s side or the father’s side, the Gemara enters into a discussion of a difficult case – the identity of the pseudo-priest in the story of pesel Micha – Micha’s idol.
According to the story at the end of Sefer Shoftim (chapter 17), during a period when “there was no king in Israel, every man did that which was right in his own eyes,” a man named Micha stole money from his mother, who then gave it to him to create an idol. When a Levite from Bethlehem in Yehuda came calling, Micha was pleased to have a Levite serve as priest in his temple.
Our Gemara points to the fact that the passage (Shoftim 17:7) identifies him as a Levite – so apparently his father was from that tribe – yet he is also identified as being from the tribe of Yehuda, so apparently his mother’s tribe is significant, as well. In response, Rava bar Rav Ḥanan suggests that he really was from Shevet (tribe of) Yehuda, and the pasuk simply means that his name was Levi.
This suggestion is rejected out of hand, since the Tanakh clearly identifies the Levite as Yehonatan ben Gershom ben Menashe (see Shoftim 18:30). The Gemara concludes that even this passage is unclear, since Yehonatan, the Levite, was not the grandson of Menashe, rather he was the grandson of Moshe Rabbeinu. Rather, the navi chose to identify him with Menashe, since his behavior was similar to that of Menashe, the evil king of Judea; in a like manner, he was identified as coming from the tribe of Yehuda, the tribe from which King Menashe came.
As the Rashbam points out, a clear indication that this pseudo-priest was a descendant of Moshe is that the letter nun of Menashe in Sefer Shoftim 18:30 is left hanging, suggesting that it should not be read, leaving the pasuk clearly identifying Yehonatan as the son of Gershom, the son of Moshe.