출애굽기 12:20의 주석

מחמצת לא תאכלו THAT WHICH LEAVENETH YE SHALL NOT EAT — Here we have the prohibition regarding eating שאור (that which causes food to become leavened).

ANYTHING THAT IS LEAVENED YE SHALL NOT EAT. “This includes food with which leaven is mixed.” Thus the language of Rashi.
This too is not in accordance with the final decision of the law, for the adopted opinion is like that of the Sages who say that the penalty incurred for eating leavened food is extinction, but for food with an admixture of leaven, there is no specific verse that includes it, [although it is nevertheless forbidden].²²⁵Why then did Rashi interpret the verse in accordance with the opinion of a single Sage — Rabbi Eliezer — when the Sages who are the majority differ with him? Commentators, however, have shown that the accepted final decision of the law in this case is in accordance with the opinion of Rabbi Eliezer. Maimonides and other scholars have all accepted the decision of Rabbi Eliezer. See my Hebrew commentary, p. 333.

בכל מושבותיכם תאכלו מצות, even outside the city of Jerusalem, although the Passover itself must not be slaughtered outside Jerusalem.

This is the warning against the eating of yeast. For the punishment was already learned from (v. 19), “Whoever eats chametz that soul shall be cut off. . ..”

בכל מושבותיכם תאכלו מצות, “you are to eatunleavened bread in all of your dwellings.” The reason why the Torah uses the expression: בכל מושבותיכם, “wherever you will be at home,” is because this commandment applies equally in the land of Israel and outside of it. This is distinct from eating of the Passover lamb, a law which can be fulfilled only in the land of Israel and at a time when offerings can be offered in the Temple or at least on the Temple Mount.

כל מחמצת [YE SHALL NOT EAT] ANYTHING THAT LEAVENETH — The use of the word כל, anything (even in the smallest degree), is intended to include food with which it (שאור) is mixed (Mekhilta d'Rabbi Yishmael 12:20:1).

Includes its mixture. Re”m discussed Rashi’s comment at length and found difficulty with it. But see Maseches Chulin 43a, and the commentary of Rashi and Tosafos there (beginning with והא אמר רבי יוחנן ), discussing the Mishnah of אלו כשרות . Re”m found difficulty with Rashi only because he overlooked this. (Nachalas Yaakov)

בכל מושבתיכם תאכלו מצות IN ALL YOUR HABITATIONS SHALL YE EAT UNLEAVENED BREAD — This statement is intended to teach that it (the unleavened bread which you must eat on the first night of Passover) must be fitted to be eaten in all your habitations, thus excluding leavened bread which forms “the second tithe” and the unleavened meal cakes brought with the thanksgiving offering (which might be eaten only within the walls of Jerusalem) (Mekhilta d'Rabbi Yishmael 12:20:2).

This comes to teach. . . Rashi is answering the question: It is obvious [that the mitzvah of matzoh applies in all places], for matzoh is an obligation upon the person, [not upon the land], and therefore applies both in Eretz Yisrael and outside it. Rashi answers: “This comes to teach. . .”

This excludes Maaser Sheni and the breads of the thanksgiving korbon. Rashi is saying that even if these were eaten in Jerusalem one cannot fulfill his obligation of eating matzoh — since they may not be eaten “in all your dwellings.”