Karpas represents spring and new growth, rebirth and the beginning of new life.  We taste in this fresh vegetable all the potential in nature and in ourselves. 

We do not taste the vegetable alone.  We dip it into salt water, recalling the tears our ancestors shed during their long years in slavery.  We mix bitterness with sweetness, slavery with freedom, past with future.

haggadah Section: Karpas
Source: A Night of Questions: A Passover Haggadah