The 4 key elements of the Seder night are:

Korban Pesach, Matzah, Maror & Daled Kosos.

Maror cleanses our bodies from grime and sin.

The Korban Pesach lifts us out of the rut and places us in an elevated place.

Matzah is spirtual food that allows the body to become more spiritual.

4 cups of wine knock out the 4 forces of evil that exist in the world. They represent the 4 lights that emanate from the Divine Name.

Each year, we take another blow at evil and eventually evil will cease to exist.

Afikoman is the final thing we eat, because we want the spiritual light we received on the Seder night to linger and last for the entire year.