The Shabbos before Pesach is named Shabbos Hagadol. The exodus from Mitzrayim was on the 15th of Nissan on a Thursday. On the tenth of Nissan which was Shabbos, Yisrael were commanded to take the lamb which was the idol worshipped by the Egyptians. When the Yidden took the lamb from the Egyptians they were questioned what they were going to do with it? They answered we are going to slaughter it for our G-d. Instead of reacting by killing the Yidden immediately for their blasphemous intent, they stood frozen in their places and could not even open their mouths. This was the great miracle that happened on that Shabbos (Tur Orach Chaim). The question in this interpretation presents itself as to why is Shabbos part of this miracle that designates every year this special day, and not rather the tenth of Nissan whichever day it falls on?

Chazal say (Baba Metziah 12) an adult over 13 who depends upon support from his father for sustanence is deemed a minor קטן, and a minor who is independent from this father is called an adult גדול. These relationships concerns dependency on physical parents. However the same applies to one's relationship with Hashem. There are two approaches to mitzvah observance. One where the Yid depends on his Father in Heaven to tell and command him all his obligations. In this scenario what is communicated to him he righteously observes and however the unspoken word is not fulfilled. The status that such a Yid possesses is that of a קטן which relies on his father. In contrast is the oveid Hashem called גדול who fulfills the desire of Hashem even though one was not asked or commanded to do more than what was told to him. This ovied's outlook is לתת נחת רוח ליוצרו to give nachas to his Creator. Such an individual reads between the lines and fulfills the spirit of the law even if it was not directly commiunicated to him. it is because one senses the drift of Hashem's desires and he takes upon himself to do everything to Hashem that would bring to Him contentment and pleasing. As the Mesilas Yesharim writes chapter 18;

שורש החסידות הוא מ"ש שאמרו חכמינו (ברכות יז) אשרי אדם שעמלו בתורה ועושה נחת רוח ליוצרו. וכתב עוד שאילו יגלה אביו את דעתו גילוי מעט שהוא חפץ בדבר מן הדברים, כבר ירבה הבן בדבר ההוא ובמעשה ההוא כל מה שיוכל ואף על פי שלא אמרו אביו אלא פעם אחת ובחצי דיבור הנה די לאותו הבן להבין היכן דעתו של אביו נוטה לעשות לו גם את אשר לא אמר לו בפירוש כיון שיוכל לדון בעצמו שיהיה הדבר ההוא נחת רוח לפניו ולא ימתין שיצוהו יותר בפירוש עכ"ל.

The first case of oveid Hashem is likened to an eved servant, and the second is compared to a son as the passuk says בנים אתם לה' אלקיכם . This relationship of Banim with Hashem must be part of the Chinuch that oine must transmit to his children as the passuk says in Mishlei חנוך לנער על פי דרכו גם כי יזקין לא יסור ממנו. The acronym of the word לנער is לתת נחת רוח ליוצרו . One can even read the passuk חנוך לנער על פי דרכו גם one must teach his child to relate to Hashem with love to go beyond the call of duty דרכו)) that he was taught, so that he will be a גם person one who does extra and adds on even the unrequested items that would bring nachas to the one whom you love.

The eved relationship is called a קטן because he depends and waits for his master to communicate to him his desire. The son father relationship is a גדול for without even being told explicitly he knows his father's unspoken desire and strives to please Him in every way possible. (הושע יא א) כי נער ישראל ואהבהו When Yisrael serves Hashem in the fashion of נער which is gematria ,גם and the acronym of ,עושה נחת רוח the father reflects a special love to his son for expressing his love to his him.

The Chasam Soffer דרוש לשבת הגדול תקמט comments on the passuk (Shir Hashirim) חדשים גם ישנים דודי צפנתי לך that Am Yisrael glorifies themselves from the fact that they added to the Torah's regiment of Pesach so many extras that the new additions exceed the original G-d given commands. Chachamim added the mitzvah of drinking four cups of wine paralleling the Four Expressions of geulah. Who instructed them to do so? They only did it because they felt an outpouring of love and deep gratitude to their Redeemer. Who commanded Yisrael to eat the Afikomen as the last food eaten at the Seder in order to ensure that the taste of the Matzah should be remembered as long as possible. It was Yisrael's relationship of בנים that inspired them to go beyond the requirement and demonstrate our dedication to serving Him. The entire Seder which we experience every year from Kadeish to Nirtza is composed from hundreds of additions that generations have added to it over the years.

Our entire redemption from Mitzrayim was based on the extras that we showed to our beloved. כזה היה כל יציאתנו ממצרים בזכות שהוסיפו יותר ממה שנצטוו We listened to Hashem's command to take the lamb to our houses on the tenth of Nissan but we tied it to our beds for four days and did not conceal our intentions of slaughtering it from our oppressors. By doing so they we were willing to be mosair nefesh and risk their lives in order to sanctify Hashem. Who asked them to do it and extend themselves to that extent? The very beginnings of the Jewish Nation was formulated by fulfilling Hashem unspoken words. Avraham Avinu discovered Hashem and created ways of avodah to serve Him before he had received any mitzvah commandments from Hashem. All of this is because Yidden have an overflowing love to Hashem which they portray by being maximally creative in mitzvos to enhance their relationship with Hashem. The term used to express a minimum fulfillment of a mitzvah is .דיעבד It has the root word עבד to convey that a non loving bond with Hashem gives you the status of an eved who would rather choose to get away with the minimum in contrast. This is in contrast with the בן who is creative with his relationship in order to invest his maximum efforts into his affinity with His Creator.

With this we can answer why that Shabbos in Mitrayim on the tenth of Nissan it acquired the adjective of גדול. This title is not referring to the day itself but rather to Bnei Yisrael who on that Shabbos graduated from the status of קטן to the status of גדול an individual who goes beyond the call of his instructions and duties. As Bnei Yisrael took the lambs for the Korban Pesach and tied it to their beds they were publicly advertising their emunah, bitachon, and avodas גם in Hashem on a maximized level. If you take the gematriah of גם with its inner letters which are גימל מם עה"כ it comes up to היא פסח. They possessed the title of גדולים who took avodas Hashem into their own hands without waiting for directives from Hashem in order to please Him.

We find that Shabbos is also called the title of גדול as we say in Birkas Hamazon כי יום זה גדול וקדוש לפניך. We also mention in the Shirah of Shabbos מה גדלו מעשיך ה' which is in contrast to what we describe during the week as .מה רבו מעשיך ה' Shabbos because of its giving to a Yid a neshamah yesairah, creates a window of accessibility to serve Hashem in the capacity of giving נחת רוח. As the Medrash says;

(ויק"ר ג א) על הפסוק (קהלת ד ו) טוב מלא כף נחת ממלא חפנים עמל ורעות רוח. אמר ר' חייא בר אבא טוב מלא כף נחת זה יום השבת, ממלא חפנים עמל אלו ששת ימי המעשה תדע לך שכן שאין ישראל נגאלין אלא בזכות שבת שנא' (ישעיה ל) בשובה ונחת תושעון

A spoonful of nachas is goodness. This is referring to the day of Shabbos. It is better than a handful of toil and bad spirit. This is referring to the week. We see from this Chazal that Shabbos sends a gift of nachas which is given back to Hashem. Chazal say (Shabbos 86) that the Torah was given on Shabbos. According to what we said above this has come to relate that all mitzvos should be fulfilled in the same spirit of a relationship of לתת נחת רוח as a "gadol" who reads between the lines and hears the spirit of law not just what it says. מלא כף נחת with its three words equals .תורה עה"כ also נחת לבוראו equals שבת עה"כ.

The Shabbos davening, Halachos, and seudos that we have in our generation has been a product of continuously upgrading over centuries to make our Shabbos a day that expresses our love to Hashem לתת נחת רוח לבוראי . The Nusach of הודו לה' before Mincha of Erev Shabbos, the lighting of candles, the Yedid Nefesh before Kabbalas Hashabas, the Pirkei Tehillim starting לכו נרננה, the Lecha Dodi, the Anah Bekoach, Mizmor Shir, Hashem Malach, Bameh Madlikin, כגוונאfrom the Zohar, a second ויכולו after Shemoneh Esrai. Shalom Aleichim Aishes Chayil, Zemiros, Shir Hamaalos before benching. Kerias Hatorah, Haforah, etc. All the different foods that we are accustomed to partake from today at the Shabbos meals etc, all the varying Hilchos Shabbos beyond thirty nine melochos etc. All of the above were not introduced to Klal Yisrael at the same period but rather at different times from different instituters that felt the inner drive to serve Hashem in the highest levels of giving נחת רוח to Hashem. They all added and added to the soul of Shabbos which we bring into are lives once a week in order to enable us in creating a deeper bond with Hashem.

Now we can see what role Shabbos played on the tenth of Nissan. It helped Yidden to graduate from the status of a katan into the status of a גדול and thereby merit Yetzias Mitzrayim as the Chasam Sofer wrote. "Shabbos Hagadol" – it was Shabbos which was instrumental in causing our redemption by nurturing us with giving to Hashem the ultimate avodah of נחת רוח.That is why it is called Shabbos Hagadol.