“….And there was thick darkness over the entire land of Egypt…” – Shemot 10:22

וַיְהִי חשֶׁךְ אֲפֵלָה בְּכָל אֶרֶץ מִצְרַיִם – שמות י, כב

Rashi notes that one of the purposes of the Plague of Darkness was to allow for the Egyptians’ homes to be searched by the Jews. This would enable the fulfillment of G-d’s directive (Shemos 3:22 and 11:2) that Bnei Yisrael empty Egypt of its valuables when they leave. “When they were leaving Egypt and requested these items, the Egyptians told them, ‘We have nothing.’ The Jews would reply, ‘I saw it in your house, and it is in such-and-such a place.'”

A similar account is found in the Midrash (Shemos Rabbah 14:3), but the Midrash adds that the actual canvassing of the Egyptians’ homes was not done in a natural way. Rather, “wherever the Jews went, light would follow them and illuminate and show all that was in the barrels, closets, and hidden recesses of the Egyptian homes.” Inherent in Rashi’s words, however, is the assumption that though Bnei Yisrael’s search was facilitated by the miraculous blinding of the Egyptians through the Plague of Darkness, it was still necessary for them to comb the Egyptian homes using natural means.

Rashi’s opinion that the search was conducted in an ordinary way, without the guidance of a miraculous light, demonstrates that the natural processes required for a mitzvah’s performance are a significant part of the mitzvah as well. The purpose of the performance of a mitzvah is to elevate the material world and transform it into a place that is G-dly and holy. Along with the actual object with which the mitzvah is fulfilled, all the physical means that bring about the mitzvah’s performance are also sanctified. Likewise, the natural hardships or monetary cost of doing a mitzvah provide for an even greater area of our lives to be elevated and included in this holy act. If these costs would be circumvented through supernatural means, the mundane and natural world would remain unaffected.

Therefore, Rashi maintains that the mitzvah assigned to Bnei Yisrael, to request and be given the Egyptian’s valuables, would be best fulfilled if it was made possible through the effort and strain of conducting a search the ordinary way. If the Jews had been shown the “hidden recesses” of the Egyptian homes by a miraculous x-ray, the opportunity for this mitzvah to elevate the natural processes of life would have been lost.

—Likkutei Sichos, vol. 31, pp. 48-49; and vol. 5, pp. 80-81