Great question. In fact, on a basic level, that is exactly why we do it—so you should ask the question “why?”

When the Torah instructs us to retell the story of the Exodus at the Seder, it phrases the commandment as a hypothetical conversation between parent and child: “If your son asks you in time to come . . . you shall say to your son, ‘We were slaves to Pharaoh in Egypt, and the L‑rd took us out of Egypt with a strong hand.’”1 The sages thus understand that the telling over of the story of the Exodus is meant to be in a question-and-answer format. (And even if there is no child to ask the questions, you do so yourself.)

The sages therefore instituted a number of rituals during the Seder for the sole purpose of arousing the child's curiosity and prompting questions.2

One of these rituals is the dipping of the karpas.

We take a vegetable that would normally only be eaten as part of a meal, dip it and eat it before the meal—thus prompting the child to ask why we are doing things differently tonight.

The common custom is to dip the vegetable into salt water (or vinegar), symbolizing the tears the Jews shed during their servitude.

By dipping the vegetable, we also get a bonus Passover question—“Why are we washing our hands before eating the karpas?”

Washing Before Eating Wet Vegetables

We’re only used to washing our hands before eating bread, so this step of the Seder, urchatz, seems unusual. However, it may be surprising to learn that this ritual is not limited to the Seder—according to the Talmud, “any food that is dipped into a liquid requires washing of the hands before it is eaten."3

The commentaries explain that even those who aren’t particular about washing for dipped foods year-round (for reasons beyond the scope of this article) do so at the Seder night since a) this dipping is more significant, since it is done as part of the Seder and is therefore treated with more respect and stringency;4 and b) this night is all about arousing questions, and therefore, the very fact that you are doing something different will lend itself to an additional question.5

Now, technically, you only need to wash if you will be eating wet food with your hand, so it is ideal to eat your karpas with your hands, thus warranting the washing that precedes it.6 Nevertheless, if for whatever reason you use a fork, you should still wash your hands.7

The Name Karpas

The Talmud does not specify which vegetable should be dipped, and in fact any vegetable may be used, other than those that may be used for the maror. However, many have the custom to use a certain vegetable by the name of karpas,since the word karpas (כרפס), when reversed, can be read as ס' פרך. The letter samach has the numerical value of 60, and perach means “hard labor,” so the word karpas alludes to the sixty myriads of Jews (600,000) who were enslaved with hard labor.8

But which vegetable is identified as karpas? Some say it is a leafy green like parsley or celery. Yet, many have the custom to use root vegetables such as potatoes, radishes and onions. The Chabad custom is to use onions or potatoes.

No After-Blessing

When we make the blessing of ha’adamah on the karpas, we have in mind that the blessing be for the maror as well. Therefore, when we eat the karpas, we should make sure to eat less than an ounce (or a whole vegetable), which may require one to make an after-blessing. (Nevertheless, if one did eat more than an ounce -as some have the custom to do- one should still not make an after-blessing.)9

The Mystical Paradox of Dipping

On a mystical note, dipping food is an act of negation—some of the food’s own taste is negated in order to receive the taste of the dip. In fact, the Hebrew word for “dipping,”טיבול, is an anagram for the Hebrew word ביטול, “nullification or negation.” Conversely, the act of dipping food demonstrates that one is a connoisseur who understands that the food on its own is lacking and knows just what to add to get the right flavor.

However, the dipping on the night of the Seder is “different than all other nights.” For on this night, even our act of dipping is a sign of negation and humility. Although we are celebrating our freedom, we are at the same time celebrating our birth as a nation in service of G‑d. And as we celebrate the exodus from one exile, we pray for our exodus from this one as well.10