The Tur writes in סימן ת\"ל that the specialty of that Shabbos is because the year when the Yidden went out of מצרים, that Shabbos came out on the tenth day of Nissan. Hashem had commanded the Yidden that on the tenth day of Nissan, they should take the שה, the sheep, and be מקריב it later on on the fourteenth day as a קרבן פסח. We all know that in מצרים, the sheep was avodah zarah, and therefore, when the מצריים saw that the Yidden took the sheep, and they found out that the reason they took it is in order to שחט it as a קרבן to Hashem, we could imagine how the מצריים felt, and what they would really have wanted to do to the Yidden. And nevertheless, there was a miracle that they couldn't say anything, they couldn't do anything, and as the lashon of the Tur is, והיו שיניהם קהות, their teeth hurt them. And we could imagine how they wanted to harm the Yidden, and stop them from doing this, and nevertheless, they weren't able to do a thing. So, this is a special miracle, and therefore we have the special day called Shabbos Hagadol. But Tosafos in שבת דף פ\"ז עמוד ב' gives a slightly different reason why it's called Shabbos Hagadol. He says because there was a miracle that happened on that day, because as we said, that's the day the Yidden took the קרבן פסח. So when the מצריים saw that the Yidden are taking a sheep, so the bechorim of מצרים came to the Yidden and asked them, why are they doing this? So they answered, this is going to be a קרבן פסח to Hashem, and Hashem is going to kill the firstborn of the מצריים. So the firstborn מצריים went to their fathers and went to פרעה, and asked them, send out the Yidden, because they were afraid for their life, and they didn't want. So the bechorim made a מלחמה, made a war, against the מצריים, and they killed many of them. And this is the meaning of the pasuk that it says למכה מצרים בבכוריהם, that they did kill the Mitzrayim through their own bechorim, because at this point, the bechorim of the Mitzrayim made a war against the Mitzrayim themselves and killed many Mitzrayim. And since that day was Shabbos, so they made a זכרון to that nes, that always the Shabbos before Pesach should be a special Shabbos and we call it Shabbos Hagadol, because a nes gadol, a big miracle happened on that day, and therefore this is called Shabbos Hagadol, the big Shabbos. But the question that's asked is, why did they establish to remember this nes on the day of the week, on Shabbos, rather than on the day of the month? We know that when Hashem established Yomim Tovim as a zecher to certain miracles that happened, it's always on the day of the month. Pesach is on the fifteenth day of Nisan because that's the day of the month the Yidden went out of Mitzrayim, but it is not on the day of the week. Why is it that this miracle was established to remember it on the day of the week? So the Magen Avraham in Orach Chaim סימן ת\"ל answers because the tenth day of Nisan really is a fast day, because this is the day that Miriam passed away. And it says in סימן תק\"פ that this day is supposed to be a fast day, and therefore, because it's a fast day, they didn't want to make that day into a Yom Tov, therefore they established as a זכרון, the remembrance of this nes, on the day of the week, which is the Shabbos before Pesach.

But mamash we have to understand this. First of all, we have to understand why was this miracle, the way Tosafos explains, such a big miracle? What's so special about it? Lichorah, there is no miracle here whatsoever. It was only natural that this should happen, because this that the bechorim believed the Yidden that Hashem is going to kill the bechorim, that is not a miracle at all. There is no wonder in that at all, because they saw from the previous cases that whenever he warned them that there is going to be a makah, the makah came, and this happened nine times before. On the contrary, if there is a wonder here, the wonder is why Paroh and the other Mitzrayim did not agree to let the Yidden out. The reason for that was was because ויחזק השם את לב פרעה, because Hashem hardened the heart of Paro. But naturally, after all the things that happened before, it only makes sense to believe the warning. So therefore, it's only natural that the בכורים of מצרים believe the warning of the Yidden, and therefore it's only natural that they would beg their parents and Paro to let the Yidden out, and it's only natural that if they wouldn't do it, the בכורים, being afraid for their lives, would wage a war against the מצריים themselves. So this is a very natural happening, so why do we refer to this as a nes, and not just as a simple nes, but we call it a nes gadol, a big nes? And also, if at least from this big nes there would be a big תועלת for the בני ישראל, if the Yidden would have gained a lot from this thing, so then even though it's not a nes, but nevertheless, being that this brought a big תועלת for the בני ישראל, we refer to it as a nes gadol. But in truth, this brought no תועלת for the בני ישראל, because even after this happened, it didn't change the status of the בני ישראל. They still were in גלות, and Paro still wouldn't let them out, until Pesach, when there was מכת מכת בכורות, nothing changed. So there was no תועלת for the בני ישראל. According to the reason of the Tur, there was a תועלת for the בני ישראל, because the miracle was that the מצרים couldn't harm them. So there was a תועלת that they couldn't harm them. But according to Tosafos, that the miracle was that מכה מצרים בבכוריהם, that the בכורים killed some of the מצרים, so what did we gain from it? So לכאורה there is no תועלת for the בני ישראל, so there is no reason to call it גדול. So the question is back, according to this reason, what's so special about this happening, why do we refer to it as a big nes, and because of that, we make a special day, which is Shabbos Hagadol? And also, the second thing that the Magen Avraham says, that the reason they didn't establish it for the day of the month, but rather for the day of the week, is because Miriam passed away on that day, is also not so understood, because it would make sense to say, even though we're not sure, that to have a minhag of calling it Shabbos Hagadol started right away the year when this happened. And Miriam didn't pass away till 40 years later. So it would come out that first they established it on the day of the month, then 40 years later, when Miriam passed away, and they wanted to make into a יום תענית, so then they changed the kvius of remembering this miracle to the day of the week rather than to the day of the month. It is hard to say this. But in truth, even if we will not say that, even if we will say that lechatchilah it was established after Miriam passed away, and therefore lechatchilah it wasn't established on the day of the month, but on the day of the week, because of Miriam's passing away, it's still not so clear, why is it that because of Miriam's passing away and they want to make it a יום תענית, they pushed off the inyan of making it into a Yom Tov? Why shouldn't it be the opposite? Why shouldn't we say that because this day is a Yom Tov, is a special day, we shouldn't establish a fast day on that day? But this last question can be answered, because we do find that those days that were established as fast days have a power of pushing away even a day which happens to be a Yom Tov. And that's how we find that there are certain days in Maseches Taanis where it says you have to fast, so even if it would come out on Rosh Chodesh, when you are not allowed to fast מן הדין, as it says in Shulchan Aruch in the beginning of סימן תק\"פ, that on Rosh Chodesh it is a halachah you're not allowed to fast. Nevertheless, those days that were established as taaniyot in Megillat Taanit, they have the power of pushing away Rosh Chodesh, and you would have to fast on Rosh Chodesh. So certainly in this case, where the Yom Tov of Shabbos Hagadol is only a minhag, so certainly those days that were established as fast days are stronger, and therefore to push away the inyan of being a Yom Tov. But on the other hand, even though we do find a reason על פי הלכה that that day, being it's a fast day for מיתת מרים, it should have the power of pushing away the Yom Tov of Shabbos Hagadol, and therefore establishing the zikaron of that nes not on the day of the month, but on the day of the week for Shabbos, so even though we have a תירוץ על פי הלכה, but still, since we know everything in the Torah is b'diyuk, is exact, so there must be a reason why this nes has a special connection to the day of the week rather than to the day of the month, like all other ימים טובים. Even though על פי הלכה the reason is because the taanit of מיתת מרים has the power of pushing this away, but nevertheless, since it does push it away, and it is put to the day of the week, obviously there is something in the day of the week that has a special connection to that miracle.

But the answer to these questions is based on first understanding what is actually the תוכן of that nes that happened on that day, because, as we said before, it seems like there was no miracle whatsoever. It was very natural for that to happen. So in that case, what is the miracle? But the answer is that this itself is the specialty of what happened on that day. Just like we find concerning Purim, that it's brought down in many sefarim, that why is the nes of Purim so special? Because it was a nes hamelubash bateva. It was a miracle that was dressed into nature. Wasn't like the miracle of, let's say, Chanukah, when it was open miracle, that the Eibershter gave over Giborim beyad chalashim, rabim beyad me'atim, that the giborim, the strong ones, fell into the hands of the weak ones, the many fell into the hands of the few. That's a miracle which is against teva. For that to happen, Hashem had to make שדוד הטבע, as we call it, the change of nature, because it did not fit with the laws of nature. So that is something special, that shows it comes from Hashem, because it is against the nature. Purim, the way it happened, was a nes which is melubash in teva, which is dressed into the nature, because it seems as if this happened naturally: first Esther became the queen, and then Mordechai heard what Bigtan VaTeresh wanted to do, and later all the events that happened later on could be explained naturally. But nevertheless, it is a nes which was put into teva. And that's why that is even greater than the nes of Chanukah. Because here we have a combination of nes and teva. When something out of the ordinary happens, and it's a real miracle beyond nature, that shows that it comes from Hashem. Nature, a person might make a mistake and think it doesn't come from Hashem. Hashem. And that is one of the reasons why it's called teva. Teva also has a meaning from the word tavu'o, which means sunk in, because the koach of Hashem is sunk in, is hidden within the nature. When a miracle happens, then the koach of Hashem is revealed. But in nature, the koach of Hashem, the power of Hashem is hidden, just like something sinks into the water. It's there, but it's covered up, you can't see it. The same here, the koach of Hashem is there, but it's hidden, we can't see it. When a nes hamelubash bateva happens, so then what it shows is that even the teva, even the nature comes from Hashem. In other words, when we see the nature working for the צד הקדושה, working for kedushah, this brings out the koach of Hashem even stronger. Because normally, teva, which is nature that covers up on the koach of Hashem, doesn't necessarily have to work for the צד הקדושה. On the contrary, the nature of the world, there is no kedushah in the world, we have to bring kedushah into the world. But when we see that the nature works so that it helps kedushah, it helps the Bnei Yisrael, this shows that even the nature comes from Hashem, and therefore the nature really is for the צד הקדושה, helps kedushah. And that's why it says that the nes of Purim is greater than many other nisim, because it is מלובש בטבע.

Similar to that is the nes that happened at the time of Shabbos Hagadol, because as we said before, it was only natural for them to do this. So what happened here was that naturally the בכורים of Mitzrayim, who were the strong ones of Mitzrayim, and they represent the strength of Mitzrayim, because the word בכור doesn't only mean firstborn, but as the Targum Onkelos says in פרשת ויחי, קפיטל מ״ט פסוק ג, he says that the word בכור means חילי וראש תוקפי, the strength and the beginning of the תוקף of the strength. So בכורי מצרים represent the strength of Mitzrayim. And in this case what happened, the בכורי מצרים, which represents Mitzrayim which is against Hashem and against kedushah and against the Bnei Yisrael, started working for the sake of the Bnei Yisrael, and it started doing this naturally. If it would have been a real open miracle, then we would know that since a miracle comes from Hashem, so obviously it will work for the sake of Hashem, it'll work for the צד הקדושה, it'll work for the Bnei Yisrael. But nature, and especially the way it was at that time, that the way the Mitzrayim were were against the Bnei Yisrael, and here, naturally, the בכורים which is the תוקף of Mitzrayim, started working for the benefit of the Bnei Yisrael, this shows the gedulath of Hashem, this shows the greatness of Hashem, that even the nature is also controlled by Hashem. והראיה, here you see that the nature is working for the Bnei Yisrael. And in one way, this is even more than it was by the nes of Purim. Because by the nes of Purim, even though it was מלובש בטבע, it was put dressed into the nature, nevertheless, it was obvious that there are things happening here out of the ordinary, that all these coincidences, so to speak, that happened, that Esther became the malka, and then Bigtan vaTeresh, and then with Haman and Achashverosh, and Mordechai, and all the different things the way the sequences of events went, all this pointed that there is something special here. So even though it was מלובש בטבע, but a little bit there was l'ma'alah min hateva there also. But in the nes of למכה מצרים בבכוריהם, there was no nes at all, it was only teva. And nevertheless, this teva worked for the sake of the Bnei Yisrael against the Mitzrayim. So this really shows the גדלות of Hashem. This really shows the greatness of Hashem. And the real greatness is the ענין of בלי גבול, being unlimited. This really shows the true infinity of the koach of Hashem, to show that not only is Hashem בעל הבית over teva and therefore He could change the teva, but He is so unlimited that teva itself is controlled by Him, that nature, with the laws of nature, remaining nature without any nissim, is really controlled by Hashem and does what Hashem wants, and therefore worked in this case for the sake of the Bnei Yisrael, even though at that time it should have been just the opposite.

And for this reason, too, it was established to be celebrated on the day of the week, not on the day of the month. Because the difference between the days of the week and the days of the month is understood, that the days of the week, that is the bri'ah, that is the creation. This is the nature. It says ששת ימים עשה השם את השמים ואת הארץ. Six days it took Hashem to create the shamayim and ha'aretz. ביום השביעי, the seventh day, שבת וינפש, He rested. So even though it seems like it's a rest from מעשה בראשית, nevertheless, even the seventh day is part of מעשה בראשית. It's the shleimut of מעשה בראשית, the completion of מעשה בראשית, but it's still part of מעשה בראשית. As we know through Chazal that מה היה העולם חסר? Menuchah. בא שבת בא מנוחה. That the world, the creation was still missing something, and that is rest. Came Shabbos, came rest. And this brought completion into the beriah. So the days of the week all show for the inyan of the beriah. The inyan of the months and the days of the month, that is something which is beyond the beriah. And it says Midrash Rabbah, in שמות רבה, פרשת ט״ו, י״א, משבחר הקדוש ברוך הוא בעולמו, קבע בו ראשי חדשים. That from when Hashem chose the world, that's when He established ראשי חדשים. So it comes out that this is not part of the creation itself, this is something that came a step later. The lashon is משבחר הקדוש ברוך הוא בעולמו, when He chose it. The creation is the creation itself, and then there is a stage that we call the choice Hashem made in the creation, which is something which is beyond the creation itself. And that's when the concept of ראשי חדשים came. So it comes out that the inyan of ראשי חדשים and חדשים בכלל, that has a shayachut to beyond the nature, and the inyan of ימי השבוע, the days of the week, that is the nature itself. And that is why you find that most of the ימים טובים are connected to the days of the month, because on every Yom Tov, Hashem brings into the world kedushah which is beyond the nature of the world. That's why a Yom Tov is called מקרא קודש, the word מקרא comes from the word calling, bringing, bringing down kedushah into the world, which is beyond the nature of the world. So this is connected to the days of the month, because the month is something which is beyond the creation itself, it is משבחר הקדוש ברוך הוא בעולמו. But the days of the week, that is nature itself. In this case, the nes of למכה מצרים בבכוריהם, since here the inyan was that the nature itself worked for kedushah, that's why the establishment of this זכרון הנס is not for the day of the month, but it is for the day of the week, to show that even the inyan of the days of the week, which is the inyan of nature, this also is from Hashem. And this is the meaning of this nes, and that's why it's called nes gadol, because this expresses not only that Hashem is in control of the world, of the nature, in a way that He could change the nature, but Hashem controls the nature while it is natural. And that was seen in the time when naturally the כחי דמצרים, the strength of Mitzrayim, fought against Mitzrayim and worked for the benefit of the Bnei Yisrael. And therefore, even though the Bnei Yisrael themselves got nothing out of it, but nevertheless, this itself, that כחי דמצרים naturally fought against the Mitzrayim, this itself is a נס גדול, and therefore it is called Shabbos Hagadol.