http://revach.net/lists/article.php?id=37

Section: Why?   Category: Moadim
TAGS:Leil HaSeder  matza  Pesach
7 Reasons Why We Break A Matza At The Seder
At the Seder instead of the usually Lechem Mishneh we have three matzos.  Very early on the middle matza is broken in half and sent away from the table for later consumption during Tzafun.  Why do we break the matza at the table?  Some of the reasons brought in the Otzar Divrei HaMeforshim are...

1.  L'Zecher Krias Yam Suf which split in half.  (Daas Zikeinim Shmos 12:8)

2.  Since the middle Matza will be eaten much later after the meal, we don't want to accidentally eat everything and have nothing left so we break off a piece and hide it. (Bais Yosef/Kol Bo 473)

3.  A Zecher for Chatzos HaLeila, midnight, when Hashem struck the Bechorim of Mitzrayim.  We break it into to uneven pieces because Moshe said "KaChatzos" around midnight.  We show that only Hashem can split things exactly in half.

4.  We were supposed to be in Mitzrayim 400 years but only were there 210.  Our shibud was split in two.  We split the matza in two.  The bigger piece representing the 210 years is sent away from the table to galus.  The smaller piece representing 190 years stays at the table of freedom.

5.  A quick reminder before we get caught up in Magid that we must finish on time to eat the Afikoman.  (Olelos Yehuda)

6.  L'Zecher the Bris Bein HaBesarim where the animal were split in two parts.  (Pe'er Aharon)

7.  To show that Geulas Mitzrayim was only half the geula.  The other half came when we received the torah.  (Rav Menashe Klein)