Shabbat HaGaddol is called as such because of the great miracle that occurred in Mitzrayim. Despite the Jewish people tying sheep (the gods of the Egyptians) to their bedposts, the Egyptians did not take revenge and kill them.
This was a great statement of Bitachon. The Jewish people risked their lives and relied on Hashem in a tremendous way.
The Sefer Meshech Chochma tells us that although technically this event occurred on the tenth of Nissan, it is connected to Shabbat, because Shabbat is all about Bitachon. Shabbat can only be fulfilled with bitachon and so they chose to have this lesson of Shabbat Hagaddol specifically connected to Shabbat.
When Erev Pesach falls out on Shabbat we read a special haftara- Shabbat HaGaddol ( this is according to almost all opinions), which begins with the words,
וְעָֽרְבָה֙ לַֽ֔ה' מִנְחַ֥ת יְהוּדָ֖ה וִירֽוּשָׁלִָ֑ם
The Korban Mincha will be sweet again to Hashem.
What is it about the Korban Mincha that is sweeter than any other korban?
Rav Moshe Feinstein says that there is a fundamental difference between a korban that comes from a mincha/ a flour or grain offering, and one that comes from an animal. Animals develop and thrive well without any human intervention. We feed cows when we raise them, for our own benefit, but cows are able to fend for themselves, as are all other animals.
But when it comes to wheat, it doesn’t develop into bread on its own. That needs clear, human intervention. Therefore, when a person brings a korban mincha, it is a higher statement of Bitachon, that says, “I understand that G-d is involved, even in my planting or other things that I am involved in- these things don’t happen on their own.”
That is the first bitachon statement of Shabbat Hagaddol, which, again, is all about strengthening our reliance on Hashem.
The second lesson is from the discussion between Hashem and the Jewish people. The Jewish people were claiming innocence and G-d was telling them they were not innocent. One of Hashem’s complaints was the fact that we were stealing from Hashem. When the Jewish people asked how, Hashem answered that they weren’t giving Ma’aser, and then told them the famous pasuk ( Malachi, chapter 3, pasuk י)
הָבִיאוּ אֶת כָּל הַמַּעֲשֵׂר אֶל בֵּית הָאוֹצָר וִיהִי טֶרֶף בְּבֵיתִי
Bring all the Ma’aser to the Bet Hamikdash and there will be food in My house
וּבְחָנוּנִי נָא בָּזֹאת אָמַר ה'
“Test me with this,” said Hashem
אִם לֹא אֶפְתַּח לָכֶם אֵת אֲרֻבּוֹת הַשָּׁמַיִם וַהֲרִיקֹתִי לָכֶם בְּרָכָה עַד בלי די
If I will not open for you the windows of heaven, and I will give you blessing to no end
Simply speaking, this blessing comes as a special Ma’aser rule. Normally, there is a rule that we don’t get paid in this world for our mitzvot, and that is why we can’t test Hashem; For example, we can’t do a Mitzvah such as wearing tefilin and expect to see success from it. It doesn’t work that way. We get paid in the next world for doing Mitzvot. We don’t normally see the rewards in this world. But Ma’aser is an exception. We can’t test G-d with Ma’aser.
Why?
Sefer Hachinuch explains that it’s because there are two aspects to giving Sedaka. One aspect is that it’s a Mitzvah- which will be rewarded in the next world.
The second aspect is a pasuk in Mishleh (perek יח, pasuk יז) which says,
מַלְוֵ֣ה יְ֭הוָה ח֣וֹנֵֽן דָּ֑ל ֹ
When you give a poor person money, you are loaning G-d the money. It’s like Hashem is saying that He’s short on cash, and asking you to lay out the money for Him. He will pay you back later.
When we give Ma’aser or Sedaka, we are laying out money for G-d. It’s a financial deal. When G-d says He will pay us back in this world, He’s not paying us for the Mitzvah, He’s paying us back for the loan. That is how the Sefer Chinuch explains this.
But the Hovot HaLevavot seems to have a different explanation.
In Shaar HaBitachon, one of the sources he cites, for Bitachon, from the Torah is this pasuk: וּבְחָנוּנִי נָא בָּזֹאת
Give Ma’aser and test Me
The Hovot HaLevavot explains this to mean that because you are giving Ma’aser, and relying on Hashem, you will get paid back. It’s not that Ma’aser is an exception, it’s that bitachon is an exception. When you rely on Hashem and He gives you something, you aren’t getting that because of your Mitzvot. You are getting it because that’s the way G-d set up the world. If you rely on Him, the reliance itself is the cause to get. It is not a reward for a mitzvah. When you give Ma’aser, you’re exercising your bitachon muscles. That bitachon is what brings about the beracha.
These are two very powerful Bitachon lesson, that we read on Shabbat Hagaddol, because that is what Shabbat Hagaddol is all about- about strengthening our bitachon, every Shabbat, but especially on the first Shabbat where the Jewish people collectively demonstrated their bitachon, and tied the sheep to their bedposts.
Have a Shabbat Hagaddol Shalom
( as in brought down by the Chida, one should not Shabbat shalom this week, but rather Shabbat Hagaddol Shalom)