Midrash su Salmi 118:15

... Teach us, our master, from when does the mitzvah of the Channukah lamp begin? Our rabbis taught – from when the sun sets until the majority of people are gone from the marketplace. And where are they to be lit? If one lives on an upper floor with a window facing the public domain, light there. If it is a time of danger, light within your house [and it is forbidden to do work by its light. R’ Asi said] it is forbidden to see by its light. Why do we light Channukah lamps? When the Hasmonean High Priest defeated the Greeks, as it says “For I bend Judah for Me like a bow; I filled [the hand of] Ephraim, and I will arouse your children, O Zion, upon your children, O Javan; and I will make you as the sword of a mighty man,” (Zechariah 9:13) they entered the Holy Temple. They found there eight iron stakes, fixed them in the ground and lit lamps upon them. Why do we read the Hallel psalms of praise? Because it is written “The Lord is God, and He gave us light.” (Tehillim 118:27) Why don’t we read it on Purim? It is written “…to destroy, to slay, and to cause to perish the entire host of every people and province that oppress them…” (Esther 8:11) and we don’t read it except to mark the fall of a kingdom and the kingdom of Ahasuerus still stood. But when the Holy One destroyed the kingdom of Greece they began to sing hymns and praises and to say that in the past we were servants to Pharoah, servants to Greece and now we are servants to the Holy One “Praise, you servants of the Lord…” (Tehillim 113:1) How many channukot (dedications) were there? There were seven. The dedication of heaven and earth, as it says “Now the heavens and the earth were completed…” (Bereshit 2:1) What dedication was there then? “And God placed them in the expanse of the heavens to shed light upon the earth.” (Bereshit 1:17) The dedication of the wall, as it says “And in the dedication of the wall of Jerusalem…” (Nechemiah 12:27) The dedication of those who came up from the exile, as it says “And they offered up for the dedication of this House of God…” (Ezra 6:17) The dedication of the priests, which we light for. The dedication of the world to come, as it says “And it shall come to pass on that day, that I will search Jerusalem with candles…” (Tzephaniah 1:12) The dedication of the princes “This was the dedication offering of the altar…” (Bamidbar 7:84) The dedication of the Sanctuary, which this is speaking of “A psalm; a song of dedication of the House, of David.” (Tehillim 30:1) Another explanation. There are seven channukot. The dedication of the creation of the world, as it is written “Now the heavens and the earth were completed…” (Bereshit 2:1) Completion is the language of dedication, as is written “All the work of the Mishkan of the Tent of Meeting was completed…” (Shemot 39:32) The dedication of Moshe, as it is written “And it was that on the day that Moses finished erecting the Mishkan…” (Bamidbar 7:1) The dedication of the House, as it is written “A psalm; a song of dedication of the House, of David.” (Tehillim 30:1) The dedication of the Second Temple [as it says “And they offered up for the dedication of this House of God…” (Ezra 6:17) and the dedication of the wall] as it says “And in the dedication of the wall of Jerusalem…” (Nechemiah 12:27) The current one of the House of Hasmonean. The dedication of the world to come, because even that has lights, as it is written “And the light of the moon shall be like the light of the sun, and the light of the sun shall be seven-fold as the light of the seven days…” (Isaiah 30:26)

(Exodus 13:3) "This day you go out in the month of Aviv (spring)": Let this not be written (i.e., Why is it needed?) (To signify) a month that is kasher — neither burning sun nor (heavy) rains. And thus is it written (Psalms 68:7) "G d settles the solitary in their homes. He takes out the bound bakosharoth." What is the intent of "bakosharoth"? A month that is kasher for you. Neither burning sun nor (heavy) rains. R. Nathan says "bakosharoth": These (the Egyptians) crying ("bacho"); the others (Israel) singing ("meshorerim"). The Egyptians crying, viz. (Numbers 33:4) "And the Egyptians were burying, etc." And Israel singing, viz. (Psalms 118:15) "A sound of song and salvation in the tents of the righteous." (Ibid.) "The right hand of the L rd is uplifted" — over Egypt. R. Nathan says: "bakosharoth" — by the deeds of the "kesheiroth" (the virtuous women) among them. Rebbi says: in the merit of the mirrors of "the congregating women," viz. (Numbers 38:8). R. Elazar b. Azaryah says: In the merit of our father Abraham He took them out of Egypt, viz. (Psalms 105: 42-43) "For He remembered His sacred word to Abraham His servant, and He took out His people in gladness, His chosen ones, in song." R. Shimon b. Yochai says: He took them out in the merit of (the mitzvah of) circumcision, viz. (Ezekiel 16:6) "And I passed by you, and I saw you steeped in your blood, etc." Variantly: With zeal (that of the L rd) did Israel leave Egypt, viz. (Exodus 13:3) "For with strength of hand did the L rd take you out of here." Variantly: With their own zeal did they leave Egypt, viz. (Ibid. 12:15) "And thus shall you eat it, your thighs, girded (ready for the road), etc." Variantly (Psalms 68:7) "G d settles the solitary in their homes. He takes out the bound bakosharoth. But rebels dwelling in dryness, etc.": They were rebels, in spite of which He dealt with them with "kashruth." And thus is it written (Ezekiel 20:7-9) "And I said to them: Let each of you cast away the abominations of his eyes, and do not defile yourselves with the idols of Egypt … and they rebelled against Me and would not listen to Me. They did not cast away the abominations of their eyes and they did not abandon the idols of Egypt … But I wrought for the sake of My name, that it not be profaned in the eyes of nations in whose midst they were, having made Myself known to them before their eyes to take them out of the land of Egypt." They were rebels — but He dealt with them with "kashruth."

Another explanation of the word bekosharot. R. Jonathan said: It may be read as beki (“to cry”) and shirot (“to sing’), that is, for those who wept and for those who sang. The Egyptians wept because there was not a single home without death in Egypt, and the Israelites sang: The voice of rejoicing and salvation is in the tents of the righteous; the right hand of the Lord doeth valiantly (Ps. 118:15). Rabbi maintained that the Hebrew word bekosharot indicates that the Holy One, blessed be He, dealt charitably (kashirot) with the Israelites, for it is said: The rebellious dwell but in a parched land (Ps. 68:7). Although they were rebellious, He treated them charitably. In the month of Abib indicates that they began to intercalate the year at that time.¹⁶The leap year was introduced so that Passover would occur in the spring. See Etz Joseph on Tanhuma, Bo 11.