The third cup of wine symbolizes the hope of freedom in that we are 3/4 of the way done with the seder. After crossing the sea, the Iraelites knew that 3/4 of their troubles were over. They were no longer slaves, that were forced to work for pharoah. However they still had a dessert to cross in hopes of reaching the land of milk and honey that is Israel today. Let's drink this third cup of wine to being 3/4 done with the seder, and being 3/4 free. 

Barukh atah Adonai, Eloheinu melekh ha'olam, borei pri ha'gafen.

haggadah Section: Bareich
Source: original