QUESTION: The Gemara discusses when a Ger Mitzri is permitted to marry a Jew and become a full member of the Jewish people. The Torah states that the third-generation descendant of a Ger Mitzri is fully accepted into the Jewish people (Devarim 23:9). The Gemara explains that the verse uses the term "Lahem" twice. One of those terms teaches that the count of the three generations begins from and includes the original convert.
The Gemara continues and says that it is necessary for the verse to say both "Asher Yivaldu" ("who will be born") and "Lahem" ("to them"). Had it said only "Asher Yivaldu," one might have thought that there must be three generations of descendants after the original convert, and only the third generation of descendants -- which is the fourth generation when the original convert is included in the count -- is permitted. "Lahem" teaches that the third generation, which is the second generation of descendants (i.e. the original convert's grandchildren), is permitted. On the other hand, had the verse said only "Lahem," one might have thought that if a pregnant woman converts, the fetus -- together with the mother -- is considered the first generation of converts. Therefore, the Torah says "Asher Yivaldu" to teach that the fetus is considered the second generation, and the children it later bears are permitted to marry into the Jewish people.
RASHI explains that when the Gemara says that both "Asher Yivaldu" and "Lahem" are necessary, it means that one should not think that "Asher Yivaldu" contradicts "Lahem" and implies that only the third generation of descendants (not including the original convert) is permitted. Rather, "Asher Yivaldu" means something else entirely and does not contradict "Lahem."
Why does Rashi write that the point of the Gemara is to resolve an apparent contradiction in the verse? Why would one have explained the verse in a way in which the words are contradictory?
ANSWER: Rashi is bothered by the wording of the Gemara. Normally, whenever the Gemara says "Itztrich," "it (the verse) is necessary," it means that two verses seem to teach the same thing, and one verse would have sufficed. The Gemara proceeds to demonstrate that the verses actually do not teach the same thing, but they teach two different lessons.
The words of the verse which the Gemara here discusses, however, do not teach the same (or even similar) lessons at all. On the contrary, according to the straightforward meaning of the verse, they contradict each other. "Asher Yivaldu" implies that the third generation of children (four generations from the convert himself) is permitted, while "Lahem" implies that the third generation including the convert himself is permitted. Why, then, does the Gemara use the term "Itztrich," which is normally used when two verses apparently teach the same thing?
In response to this question, Rashi explains that the Gemara's question is that there is a contradiction in the words of the verse, and not that there is an unnecessary repetition. The Gemara means that one should not think that one of the phrases in the verse implies a seemingly incorrect statement (as it contradicts the other phrase). Rather, the second verses is "needed" ("Itztrich") to teach a different Halachah altogether.