The ninth plague was the plague of darkness. The Sages relate that Israelites had light everywhere they went, even in the houses of the Egyptians. Therefore, they were able to locate items of value that they would later get from the Egyptians, and to gain their trust so the Egyptians would agree to give them those items (see below).

The darkness the Egyptians experienced was extremely intense. Our Sages say: There were seven days of darkness. How so? During the first three days, one who was sitting and sought to stand would be able to stand, and one who was standing who sought to sit would be able to sit. Concerning those days, it is stated: “There was pitch darkness in the entire land of Egypt for three days; they did not see one another” (Exodus 10:22–23). For the next three days, one who was sitting was unable to stand, and one who was standing was unable to sit, and one who was crouching was unable to stand upright. Concerning them, it is stated: “Nor did anyone rise from his place for three days” (10:23). During the first three days of pitch darkness, the Holy One, blessed be He, enabled the Israelites to find favor in the eyes of the Egyptians, so that the Egyptians would later lend items to them. When the Israelites entered the Egyptians’ houses during the days of pitch darkness, they saw silver and gold vessels and garments. If the Egyptians would later say to the Israelites, in response to their request for items: We have nothing to lend you, the Israelites would say to them: It is in such and such place. At that moment, the Egyptians would say: Had the Israelites sought to deceive us, they would have taken the items when they discovered them during the days of darkness and we would have been unaware, as they saw them already. Since they did not touch them without our knowledge, likewise, they will not keep them. The Egyptians lent the items to them in fulfillment of that which is stated concerning the Israelites, in God’s covenant with Abraham: “And afterward they will emerge with great property” (Genesis 15:14). That is what is written: “But all the children of Israel had light in their dwellings” (Exodus 10:23). It is not stated that they had light in the land of Goshen, where they resided. Rather, it is stated “in their dwellings,” teaching that anywhere an Israelite entered, light entered and illuminated for him what was in barrels, and in chests, and in closets. (Shemot Rabba 14)