פֿאַרבונדן אויף שמות 10:21

Hashem said to Moshe, "stretch your hand upon the heavens and there will be darkness in the land of Egypt". The question could be asked: Moshe was under the heaven, but he lifts his hand above the heaven--it should've said "lift your hand to the heaven." It sounds like he's on top of the heaven. The explanation is: it says in the posuk "praise Gd from the heavens...and the water that is above the heavens. Let us praise the name of Gd because He commanded and it was created and He caused it to endure forever." We need to understand what is this great praise of the water above--how come the Torah specifies that specifically? The answer is a hint to kindness, as is known. Kindness is greater than the heavens. It says in the posuk "your kindness is greater than the heavens," and kindness is beneficial when it descends into this world through a perfect tzaddik. Also, water is gematria "90," which equals, numerically, to "tzaddik." A tzaddik is a conduit from whom the Supernal Kindness [above the Heaven] descends. He does this with the power of his soul, which is in this world, but his source is in the highest of heavens. Therefore, the highest lights are able to descend through him. Just as this was for Moshe Rabbeinu, who brought good kindness and holy lights to the world. This is the inner meaning of the posuk "G-d saw the light was good, and G-d separated between the light and darkness." What this alludes to: how G-d saw and prepared the Supernal Light (which is Supernal Kindness), "His Kindness is everlasting." G-d prepared it to bring it down through the tzaddik, Moshe Rabbeinu, who's called "good" as it says in the Torah "...and she saw that he was good." Every tzaddik is also called "good," as it says in the posuk "say to the tzaddik that he is good." That's the meaning of the posuk that "G-d separated between the light and the darkness." Why does the Torah repeat G-d's name in the same posuk? This actually refers to Moshe Rabbeinu, who's referred as "Elohim" in the posuk "Look, I have given you as Elohim to Pharaoh." Moshe's also called a "man of Gd." What this means is that when Moshe serves as a vessel for G-d's kindness, he separates between the light and darkness, between the actions of the tzaddikim and wicked, so they will not be mixed up, so the Jews shouldn't go sometime in light and sometime in darkness, G-d forbid. Instead, with a power of his soul, he brings this [kindness] to the Jewish people, separating them from the Egyptians. This is the main separation of light and darkness: the separation between the Jews and gentiles. However, this Supernal Hidden Light is hidden in Shabbat, which is called a "good gift" as it says in the Talmud "I have a good gift in my storage house." So, on Shabbat this hidden Light goes down to the Jewish people, which is why we say, in Havdalah, Hashem separates between the Jews and the gentiles, immediately followed by Hashem separating the Seventh day and the rest of the week. That's why it says in the posuk "they had light where they lived (b'moshvotam) [which has the same letters as Shabbat]." What that means is that Moshe brough the Supernal Light on Shabbat, and he made all the separation between light and darkness, the Jews and gentiles, the Seventh day and six days of the week. So, when he brought the light of Shabbat to Jewish people it automatically caused the Egyptians to have darkness because they don't deserve to use that light. This is the meaning of the Midrash that the darkness he brought upon them the Supernal Darkness. There's a Moshe Rabbeinu in every generation and that tzaddik is a conduit to bring down the Supernal Light, as it says in the Torah "the light is planted for the tzaddik" and he brings it down to the Jewish people, as it verse concludes "the upright have joy." Because he brings to the upright of heart (the Jewish people), the simcha, the joy, and the tranquality, which is why tzaddikim are called "luminaries"