(From Haamek Davar on Devarim 22:8)
“When you build a new house you should build a protective fence (‘maakeh’) for your roof.” (Devarim 22:8) According to the Sifrei, this halakha also applies to an old house: “[From the beginning of the verse] I would only have known that this applies to a newly built house. What is the source obligating a bought or inherited house, or one received as a present? The word ‘house (bayit)’ teaches us that these are also obligated.” Why, if so, does the Torah speak about a new house?
The Torah is alluding to a crucial principle: A house should be built on a mitzvah foundation. This approach is brought out in a passage in the Zohar Parshat Metzora.
Why, though, did the Torah choose to teach this in conjunction with maakeh and not through mezuza? Why didn’t the Torah say, “When you build a new house place a mezuza on the door”?
The reason is because a house is more halakhically dependent on a maakeh than on a mezuza. One who is not able to obtain a mezuza is still permitted to live in the house and, when he later gets one, affixes it (see the Netziv’s Haamek Sheela on Sheilta 126:7). This is not the case for maakeh, where it is prohibited to live in a house that is obligated to have one but does not.
This d’var Torah courtesy of the David Shapell College of Jewish Studies, darchenoam.org.