Why do we eat maror? It represents the bitterness of slavery. Tradition says that by eating the herbs we feel the bitterness ourselves, and can more easily imagine ourselves as slaves. But this is not just a tradition in Judaism - it is a commandment. Both Exodus and Numbers contain the instruction to eat the Pesach sacrifice with "unleavened bread and bitter herbs." 

But we also eat the maror with haroset. Although the haroset symbolizes slave labor by reminding us of mortar for bricks our ancestors laid in Egypt, it has a sweet taste. This is to remind us that sometimes our subjugation can be masked in familiar sweetness. By eating them together, we remind ourselves that life is both sweet and bitter, and the importance of maintaining balance between the two.

Let the maror also remind us that pain is not meaningless. That the suffering our ancestors endured was not in vain. Instead, it lead to their outcry for freedom, and their commitment to their own redemption.

haggadah Section: Maror
Source: http://www.myjewishlearning.com/article/maror/