Mitzvah or Method?

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by R. Moshe Kurtz

Lomdus on the Parsha: Ki Seitzei

Based on the Acclaimed Sefer Chavatzeles HaSharon

Q: What makes something a real mitzvah?

When you build a new house, you shall make a fence for your roof, so that you do not bring bloodguilt on your house if anyone should fall from it. (Deuteronomy 22:8)

The Chasam Sofer notes that the above verse appears to be out of order. First it should establish the general principle of lo sasim damim b’veisecha, the prohibition of bringing blood upon one’s home, and then it would logically follow that one is thereby obligated to build a fence (parapet) on his roof.

(I) The Ramban, in his commentary on the Talmud (Kiddushin 34a), explains that the primary purpose of this verse is to instruct us to build a fence around our roofs. The subsequent negative commandment of lo sasim damim b’veisecha is intended simply as a means of emphasizing the gravity of this particular mitzvah. Thus, it is logical that the primary law of building a fence is mentioned first.

(II) The Chazon Ish (C.M., Likkutim 18:1) takes a different approach by arguing that the commandment to build a fence and the prohibition of lo sasim damim b’veisecha are not inextricably intertwined. The Talmud in Sukkah (3a) cites a baraisa which teaches that the definition of a house in Jewish law is four by four amos (unit of measurement):

A house which is not four cubits square is free from the obligations of mezuzah, and fence, does not contract levitical uncleanliness from leprosy, is not irredeemable among the dwelling houses of a walled city, nor does one return on its account from the array of war, nor need an eruv be prepared for it, nor shittuf, nor does one place therein an eruv nor make of it an extension between two cities, nor can brothers or partners divide it.

A structure which is less than 4×4 amos would not require a fence on its roof. (Also, the Talmud in Chullin 136a exempts synagogues and study halls from constructing a fence as well.) Why should we no longer be concerned for a danger just because the structure has smaller dimensions? If anything it may even be a great danger due to the lack of space on the roof!

The Chazon Ish explains that in addition to the general principle of lo sasim damim b’veisecha there is an independent mitzvah to construct a fence on one’s roof, even if there is no serious danger posed by the lack of it. The Chazon Ish posits that most people know to be careful when they are on an elevated surface, and that strictly speaking, there is no necessity to require a fence on one’s roof. However, the Torah was concerned for even an uncommon mishap and thus mandated that a fence should be constructed upon any structure that is classified as a house – and used the standard 4×4 amos dimensions as its threshold. 

Thus, the reason that the Torah listed the mitzvah of building a fence first was to dispel our initial impression that building a fence is simply a method for fulfilling lo sasim damim b’veisecha, but rather it is its own intrinsic mitzvah.

Let us ask a related question – should one recite a blessing upon constructing a fence on his roof?

Tosafos (Chullin 105a, s.v. Mayim) draws what seems to be a clear distinction: The Gemara states that “the first waters are a mitzvah and the latter waters are obligatory (chovah).” Tosafos explain that the reason we recite a blessing on washing prior to a meal is to commemorate the laws of purity required for consuming Terumah (sacred food for the priests), whereas the post-meal washing serves the purpose of protecting one from a particularly harmful salt and thus does not require a special blessing (see also Mishneh Torah, Hilchos Berachos 11:4.)

Based on this distinction of Tosafos, R. Akiva Eiger (Chullin 105a) is troubled by why many rule to recite a blessing on erecting a fence when, similar to post-meal washing, it simply serves the purpose of preventing harm. (Indeed, there are some who hold that there is no blessing recited on constructing a fence – see Meiri on Megillah 21b and Rokeiach no. 366.)

Based on the Chazon Ish we just reviewed, there is a clear distinction between constructing a fence and washing one’s hands after a meal. Since the imperative to create a fence is not simply a method of preventing blood on one’s property, but is its own categorical mitzvah, it would require a blessing just like any other positive commandments e.g. similar to how the Sages instituted a mitzvah on the very deed of washing before the meal. Whereas washing after the meal is more what you would call a guideline than an actual rule.

(Tosafos on Shabbos 25b, s.v. Chovah, also reckons with whether lighting candles for Shabbos requires a blessing. In Sefer HaYashar, no. 621, Rabbeinu Tam explicitly cites the position of Rabbeinu Meshulem who held that a blessing should not be recited. R. Mordechai Carlebach elucidates that since the purpose of the candles, according to Rabbeinu Meshulem, is only a method for ensuring shalom bayis – that people are not tripping in the dark and there is tranquility in the home – it would not be deserving of its own blessing since it is not a cheftza shel mitzvah, an inherently valuable ritual act, similar to washing at the end of a meal.)

Another ramification of whether something is classified as a mitzvah or method is whether one needs to fulfill the act himself (or through an appointed agent). If the purpose of a fence is simply to avoid transgressing lo sasim damim b’veisecha, as long as the result is that there is a fence there, it would be immaterial how it got there. Whereas, according to the Chazon Ish who views the construction of a fence as an independent mitzvah, perhaps it would not be sufficient if someone else builds it, unless they were appointed as an agent of the homeowner – since it is the individual (gavra) himself who is obligated in this mitzvah (see Minchas Chinuch 546:3). 

As we have seen, there is an independent value of placing a fence around one’s home to protect against even a farfetched possibility of harm befalling another human being. In a similar vein, our Sages exhorted us to “make a fence around the Torah” (Avos 1:1) so that we should not just be scrupulous in protecting our mortal bodies but, all the more so, our eternal souls. 

Note: This series is not intended to dispense practical halachic conclusions. The Torah presented here is but a small extraction from the breadth of the sefer Chavatzeles HaSharon and is not affiliated with the author in any official capacity. Translations are adapted from Sefaria,, Mechon Mamre, and my  own. Contact: [email protected] 

About Moshe Kurtz

Rabbi Moshe Kurtz is Assistant Rabbi at Congregation Agudath Sholom of Stamford, CT. He welcomes questions, feedback and speaking requests at: [email protected].

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