The history of the world is divided into four phases, Olam HaZeh, Yimos HaMoshiach, Techias HaMeisim, and Olam Haba. This is alluded to in Shabbos davening. Ein Aroch Licha... BaOlam HaZeh
V'Ein Zulasecha Malkeinu L'Chayei Olam Haba
Efes Bilticha Go'aleinu Limos HaMoshiach
V'Ein Domeh Licha Moshi'einu Lis'chiyas HaMeisim
It is said in the name of the Vilna Gaon that these four worlds are represented in the four kosos. The first kos is Kiddush. In Olam HaZeh we need to make ourselves holy and rise above the mundane world, to make the world Kaddosh as well. The second is Go'al Yisroel which is the redemption of the days of Moshiach. The third kos is Birchas HaMazon which talks about Hashem sustaining us and granting life and alludes to Techias HaMeisim. The fourth kos is Hallel which is the purely ruchniyos singing of Shira to Hashem and represents the perfect world of Olam Haba.
Click here for an updated cartoon version of the four questions asked at the seder.