"עֵקֶב תִּשְׁמְעוּן"; Reconciling the Understandings of Rashi and the Chizkuni

The Chizkuni famously did not cite his sources, except when quoting Rashi (in his introduction, he explains that he did not want some of his commentary to be given less weight based on the source; and that all of his commentary should be treated equally regardless of the source). This comment appears to be based on the Rashbam:

A key discrepancy between Rashi and the Chizkuni / Rashbam is that Rashi understands the pasuk as referring to the individual (see, e.g., "שאדם דש" and "ישמור לך"); while the Chizkuni / Rashbam posit that the emphasis is on the entire generation. Specifically, the Chizkuni / Rashbam point to the brachot being based on the conduct of the generation, and the brachot being awarded to the generation. The question is whether these two views (the charge being to the individual v. to the generation) can be reconciled?

I think perhaps that the idea of "מצוה קלה" that Rashi references is the link.

Relevant questions on this gemara: How could the gemara say that Succah does not require any expenditure? To buy the materials of a Succah is expensive! Even if we want to say that we can make a Succah from materials we already have (see Steinsaltz: "חסרון כיס, שאין צריך להוציא על כך כסף, אלא אפשר לבנות ממה שיש בידו"), re-purposing materials that we have in our possession still costs us monetary loss.

Succah is a unique mitsva that allows for communal sharing. Consider the following halachot regarding Succah:

• All of klal yisrael can theoretically share 1 succah and be yotze: סוכה כ״ז ב
  "וחכמים אומרים אע"פ שאמרו אין אדם יוצא ידי חובתו ביום טוב הראשון בלולבו של חבירו אבל יוצא ידי חובתו בסוכתו של חבירו דכתיב (ויקרא כג, מב) כל האזרח בישראל ישבו בסוכות מלמד שכל ישראל ראוים לישב בסוכה אחת"

  And the Rabbis say: Although they said that a person does not fulfill his obligation on the first day of the Festival with the lulav of another, he fulfills his obligation with the sukka of another, as it is written: “All the homeborn in Israel shall reside in sukkot” (Leviticus 23:42). This teaches that all of the Jewish people are fit to reside in one sukka. "

• A person can be yotze sitting in a borrowed Succah or in a stolen succah... or even a succah made from stolen materials; or a succah that is in the public sphere (משנה תורה, הלכות שופר וסוכה ולולב ה׳:כה):

  "סֻכָּה שְׁאוּלָה כְּשֵׁרָה וְכֵן הַגְּזוּלָה כְּשֵׁרָה. כֵּיצַד. אִם תָּקַף עַל חֲבֵרוֹ וְהוֹצִיאוֹ מִסֻּכָּתוֹ וּגְזָלָהּ וְיָשַׁב בָּהּ יָצָא שֶׁאֵין הַקַּרְקַע נִגְזֶלֶת. וְאִם גָּזַל עֵצִים וְעָשָׂה מֵהֶן סֻכָּה יָצָא. שֶׁתַּקָּנַת חֲכָמִים הִיא שֶׁאֵין לְבַעַל הָעֵצִים אֶלָּא דְּמֵי עֵצִים בִּלְבַד. וַאֲפִלּוּ גָּזַל נְסָרִים וְהִנִּיחָן וְלֹא חִבְּרָן וְלֹא שָׁנָה בָּהֶן כְּלוּם יָצָא. הָעוֹשֶׂה סֻכָּתוֹ בִּרְשׁוּת הָרַבִּים הֲרֵי זוֹ כְּשֵׁרָה:"

Perhaps HaShem is referring to the aspect of fulfilling the mitsva of succah not by focusing on the person sitting in his own succah, but by enabling others to sit in his succah. A possible hint to this is that HaShem specifically says "לכו ועשו אותה" when אותן would have been more appropriate. HaShem is highlighting that the goyim could have made one succah and then they could have participated together. Alternatively, perhaps He was telling the goyim that they should not be solely focused on their own fulfillment on the mitsva, but that they should make sure that the entire (goy) nation is fulfilling the mitsva.

In sum, succah was a "mitsva kala" because it costs nothing for a person to ensure that others can fulfill it too. With the warning of "עקב תשמעון" Moshe is teaching that in order to receive HaShem's chesed and brachot, we have to assist others in observance of the mitsvot. This message was especially important at this time because after 40 years of traveling together through the midbar, the Jews are about to split up; the shevatim would be separated, and then, within their own territories, they would be separated by families. In this new situation, each Jew might fall into the trap that it suffices that he performs the mitsvot. So, Moshe reminds them that they are still responsible for what the rest of klal yisrael is doing.

That chesed (of looking after other Jews and ensuring that they are able to and are keeping the mitsvot) is a central key to being worthy of HaShem's chesed. In that regard, it is incumbent on the entire generation to not only keep the mitsvot, but to make sure each and every individual keeps them as well. And in that regard, both Rashi and the Chizkuni / Rashbam are actually saying the same thing, just from different sides of the same coin.

This link between the aggadah in עבודה זרה and our pasuk might be that the former is referencing y'mot moshiach; i.e., a future, everlasting s'char earned by the Bnai Yisrael for following the mitsvot and several midrashim that understand "עקב תשמעון" as promising a future reward. See, e.g.,

דברים רבה ג׳:א, מדרש תהילים צ״ב:ח, ילקוט שמעוני על נ"ך תתמ״ה

This idea seems to have the support of the Sforno (based on ספרא, אמור, פרק ט) who says that when the pasuk commands us to "guard" the commandments (ושמרתם), it is a commandment to study the mitsvot (as opposed - and in addition - to the commandment "ועשיתם" which was in the same breath). This is reminiscent of another time that the bnai yisrael had the obligation to perform the mitsvot simultaneously with the obligation to study them; specifically, when they responded to Moshe "נעשה ונשמע". There (שמות כ״ד:ז׳) the Bais HaLevi says that the B'Y committed to keeping the mitsvot that they themselves were commanded and simultaneously committed to learning those mitsvot that didn't apply to them to make sure that the Jews who were obligated, would fulfill them. The Bais HaLevi concludes that the B'Y the Jews voluntarily took on the mitsva of kol yisrael arevim ze la'ze. (See, also, the Chayei Adam who cites this pasuk as a source for the mitsva to learn Torah חיי אדם י׳:א)

Perhaps that also explains why when the B'Y volunteered to learn the mitsvot, they used the softer lashon of "נשמע" but now that it is a hiyuv, Moshe uses the stronger form of "שמרתם".