When I was young my father would teach me about the Torah through debates. Before Pesach, he would tell me of  the special relationship between Moses and Hashem. In the days that Moses spent on Mount Sinai, Hashem took him through the seven heavens and Ganaden and Gaheniem (what people would consider heavenly gardens and the pits of hell). Moses was shown the most beautiful of things and the most evil.  When Moses asked why Hashem would create such evil, he was told, according to my father, that "it was none of his business". 

"Why do you think Hashem would create such evil," my father would ask.

Here is my answer:

To understand true beauty, to truly appreciate goodness and experience love, we must understand ugliness, see evil and feel hate. We must experience these things in their varying degrees to fully understand how good goodness can be, and how bad evil can be. We must search through the darkness to find the light. 

During Pesach, to appreciate our freedom, we must experience the bitterness of slavery.  Since Judaism is full of symbolism, and slavery is not something we want to actually experience, we eat maror - the bitter herb followed by charoset - sweet apples and wine.

haggadah Section: Cover
Source: Lester Kaber