The three most important pieces of the seder table are the pesach - passover offering, matzah and maror - bitter herbs. The passover offering because G-d passed over the houses of our ancestors in Egypt. The matzah because our ancestors did not have time to let the dough rise before leaving Egypt. And maror because the Egyptians embittered our ancestors' lives.
(א) טרם יחמץ. הַמִּצְרִים לֹא הִנִּיחוּם לִשְׁהוֹת כְּדֵי חִמּוּץ: (ב) משארתם. שְׁיָרֵי מַצָּה וּמָרוֹר. (ג) על שכמם. אַעַ"פִּ שֶׁבְּהֵמוֹת הַרְבֵּה הוֹלִיכוּ עִמָּהֶם, מְחַבְּבִים הָיוּ אֶת הַמִּצְוָה:
(1) טרם יחמץ BEFORE IT WAS LEAVENED — The Egyptians would not allow them to stay long enough for the dough to become leavened. (2) משארתם (from the root שאר “to be left over”) denotes the leavings (what was left) of the unleavened bread and bitter herbs
מַאן תַּנָּא דְּשָׁמְעַתְּ לֵיהּ מִצְוֹת אֵין מְבַטְּלוֹת זוֹ אֶת זוֹ? הִלֵּל הִיא. דְּתַנְיָא, אָמְרוּ עָלָיו עַל הִלֵּל שֶׁהָיָה כּוֹרְכָן בְּבַת אַחַת וְאוֹכְלָן, שֶׁנֶּאֱמַר: ״עַל מַצּוֹת וּמְרוֹרִים יֹאכְלוּהוּ״.
The Gemara asks: Who is the tanna that you heard say that mitzvot do not nullify each other? It is Hillel, as it was taught in a baraita: They said about Hillel that he would wrap matza and bitter herbs together and eat them, as it is stated: “They shall eat it with matzot and bitter herbs” (Numbers 9:11), which indicates that these two foods should be consumed together.
For children, matzah, especially the afikomen, is central to the seder. Why do we hide the afikomen and why is it the very last thing we eat at the seder?
קְלָיוֹת וֶאֱגוֹזִין בְּעֶרֶב פֶּסַח כְּדֵי שֶׁלֹּא יִשְׁנוּ, וְיִשְׁאֲלוּ. אָמְרוּ עָלָיו עַל רַבִּי עֲקִיבָא שֶׁהָיָה מְחַלֵּק קְלָיוֹת וֶאֱגוֹזִין לְתִינוֹקוֹת בְּעֶרֶב פֶּסַח כְּדֵי שֶׁלֹּא יִשְׁנוּ, וְיִשְׁאֲלוּ. תַּנְיָא, רַבִּי אֱלִיעֶזֶר אוֹמֵר: חוֹטְפִין מַצּוֹת בְּלֵילֵי פְּסָחִים בִּשְׁבִיל תִּינוֹקוֹת שֶׁלֹּא יִשְׁנוּ.
roasted grains and nuts on Passover eve, so that they will not sleep and also so they will ask the four questions at night. They said about Rabbi Akiva that he would distribute roasted grains and nuts to children on Passover eve, so that they would not sleep and so they would ask. It was taught in a baraita that Rabbi Eliezer says: One grabs the matzot on the nights of Passover. One should eat them very quickly on account of the children, so that, due to the hasty consumption of the meal, they will not sleep and they will inquire into the meaning of this unusual practice.
צָפוּן
אחר גמר הסעודה לוקח כל אחד מהמסבים כזית מהמצה שהייתה צפונה לאפיקומן ואוכל ממנה כזית בהסבה. וצריך לאוכלה קודם חצות הלילה.
לפני אכילת האפיקומן יאמר: זֵכֶר לְקָרְבָּן פֶּסַח הָנֶאֱכַל עַל הָשוֹׁבַע.
The Concealed [Matsa]
After the end of the meal, all those present take a kazayit from the matsa, that was concealed for the afikoman, and eat a kazayit from it while reclining.
Before eating the afikoman, he should say: "In memory of the Pesach sacrifice that was eaten upon being satiated."
(א) דיני אכילת האפיקומן. ובו ב' סעיפים:לאחר גמר כל הסעודה אוכלים ממצה השמורה תחת המפה כזית כל אחד זכר לפסח הנאכל על השובע ויאכלנו בהסיבה ולא יברך עליו ויהא זהיר לאכלו קודם חצות: (ויקדים עצמו שגם ההלל יקרא קודם חצות) (ר"ן פרק ע"פ וס"ב דמגילה):
At the end of the meal, we eat the guarded matza under the cover consuming an olive size in remembrance of the Passover sacrifice. We eat the matza in a reclining position and we do not say a blessing over it. One should be careful not to consume it after midnight. (One should also recite Hallel before midnight.)
...
וְאָמַר רַבִּי לֵוִי בַּר חָמָא, אָמַר רַבִּי שִׁמְעוֹן בֶּן לָקִישׁ, מַאי דִּכְתִיב ״וְאֶתְּנָה לְךָ אֶת לֻחֹת הָאֶבֶן וְהַתּוֹרָה וְהַמִּצְוָה אֲשֶׁר כָּתַבְתִּי לְהוֹרֹתָם״. ״לֻחֹת״ — אֵלּוּ עֲשֶׂרֶת הַדִּבְּרוֹת, ״תּוֹרָה״ — זֶה מִקְרָא, ״וְהַמִּצְוָה״ — זוֹ מִשְׁנָה, ״אֲשֶׁר כָּתַבְתִּי״ — אֵלּוּ נְבִיאִים וּכְתוּבִים, ״לְהוֹרוֹתָם״ — זֶה תַּלְמוּד, מְלַמֵּד שֶׁכּוּלָּם נִתְּנוּ לְמֹשֶׁה מִסִּינַי.
And Rabbi Levi bar Ḥama said that Rabbi Shimon ben Lakish said: God said to Moses, “Ascend to me on the mountain and be there, and I will give you the stone tablets and the Torah and the mitzva that I have written that you may teach them” (Exodus 24:12), meaning that God revealed to Moses not only the Written Torah, but all of Torah, as it would be transmitted through the generations. The “tablets” are the ten commandments that were written on the tablets of the Covenant, the “Torah” is the five books of Moses. The “mitzva” is the Mishna, which includes explanations for the mitzvot and how they are to be performed. “That I have written” refers to the Prophets and Writings, written with divine inspiration. “That you may teach them” refers to the Talmud, which explains the Mishna. These explanations are the foundation for the rulings of practical halakha. This verse teaches that all aspects of Torah were given to Moses from Sinai.
מִֽי־יִתְּנֵ֣נִי בַמִּדְבָּ֗ר מְלוֹן֙ אֹֽרְחִ֔ים וְאֶֽעֶזְבָה֙ אֶת־עַמִּ֔י וְאֵלְכָ֖ה מֵֽאִתָּ֑ם כִּ֤י כֻלָּם֙ מְנָ֣אֲפִ֔ים עֲצֶ֖רֶת בֹּגְדִֽים׃
Oh, to be in the desert,At an encampment for wayfarers!Oh, to leave my people,To go away from them—For they are all adulterers,A band of rogues.