신명기 4:2 해설: Rashi, Chizkuni, Da'at Zekenim & Ramban

לא תספו YE SHALL NOT ADD — For instance, to place five chapters in the Tephillin, to employ five species of fruit and plants in the fulfilment of the command of Lulab And to place five fringes on one’s garment. Thus, too, must we explain the following words ולא תגרעו, Ye shall not diminish [from it]" (Sifrei Devarim 82:4).

לא תוסיפו על הדברת ״, “do not add to the word, etc.” Moses reminds the people that when they had been told in Deut. 1,21 עלה רש “ascend and take ancestral possession,” they had added a condition of their own by requesting to dispatch spies. If they had not done so, they would have settled in the Holy Land 40 years earlier and would not have had to watch a whole generation die in the desert. Their fathers had become corpses in the desert.

לא תוסיפו וגו, “do not add, etc.;” G–d implies that anyone adding to the words of the Torah,-however well meaning he may be,-will in fact detract from the value of the Torah. [If G–d is perfect, something that every believing Jew accepts as axiomatic, any addition to or deletion from His Torah would make it, ergo Him, imperfect. Ed.] For instance, when the Torah decreed 4 strings of tzitzit for the corners of a four-cornered garment, adding a fifth string would not only not make it holier, but would make it useless, and anyone reciting a benediction over such a tallit would desecrate the holy name of G–d by pronouncing such a benediction. The same reasoning applies to sitting in a sukkah for an extra day or adding another a fifth species to a lulav.