Matzot placeholders for Pesach Seder

The three matzot that are placed on the Seder plate are referred to as Kohen, Levi, and Yisrael as a means of distinguishing them from each other.
The top matzah is referred to as Kohen, for the Kohen takes precedence in all matters.
The middle matzah Levi is broken into two at the beginning of the Seder. The smaller piece is left on the plate and is later eaten along with the Kohen matzah in fulfillment of the mitzvah of matzah; the larger piece is put away for use as the afikoman.
The bottom matzah, Yisrael is used for korech, so that every one of the matzot is used for the performance of a mitzvah.
On Shabbat and Festivals we say the blessing for bread over two loaves or matzot. Why then, on this night, do we require three Matzah is known as "the bread of poverty." A poor man, fearful lest he will have no more, guards his bread carefully. He does not eat it all at once but divides it, laying part aside for the morrow. The honor given to the Festival and to Shabbat [for often the two coincide] demands that we use two whole matzot over which we recite the haMotzi blessing "Who brings forth bread from the earth" before beginning the meal. For the blessing, "Who has commanded us to eat matzot," we use only a piece of a whole one to symbolize "the bread of poverty."