After kiddush we eat the karpas, a vegetable. The Sages ordained eating karpas to create a change that will cause the children to ask why it is that tonight, unlike all other nights, we are eating a vegetable before the meal (Rashi and Rashbam on Pesaĥim 114a). Another reason given for this is that free people generally begin their meals with a vegetable appetizer, and so we do the same at the beginning of the Seder (Maharil).
The Sages ordained dipping the vegetable in a liquid, because this necessitates washing the hands before eating it, which is also a departure from the usual order of things. Ordinarily, the hands are washed only once at the beginning of the meal before eating bread. Thereafter, a variety of other foods are eaten. However, even if we dip these other foods in liquids, it is not necessary to wash our hands a second time, because hand-washing for bread covers the whole meal. At the Seder, though, we wash once before eating the karpas and a second time after reciting the Hagada, before eating the matza. The children therefore ask: “Why is this night different that, unlike all other nights, on this night we wash our hands twice?” (Tur and Beit Yosef 473:6). In addition, dipping the vegetable in liquid gives expression to our freedom, because this is the best way to eat it: not only does it serve as an appetizer, we even pamper ourselves by dipping it in salt water or vinegar, which enhances flavor and stimulates the appetite.
A full explanation of this law lies beyond the scope of this book, but suffice it to say that liquids conduct impurity (“tum’a”) more effectively than solid foods. The Sages therefore ordained the washing of hands before eating a food that has been dipped in liquid. According to most Rishonim, this hand washing has the same status as hand washing before eating bread: both were instituted to avoid tum’a. Even though nowadays we do not observe the laws of ritual purity and impurity, the institution remains in force. Thus, just as one must recite the berakha of “al netilat yadayim” over the hand washing before bread, so must one recite this blessing before eating a food dipped in liquid. This is the opinion of Rambam and Rosh. However, according to R. Meir of Rothenburg (Maharam), Itur, and Tosafot (Pesaĥim 115a), there is a difference between these two types of hand washing: netilat yadayim before bread was instituted for purposes of sanctity and cleanliness, and thus even today hands should be washed for cleanliness before a meal. Consequently, this hand washing requires a berakha. However, netilat yadayim before eating a food dipped in liquid is only due to tum’a, and since these laws are not practiced nowadays, there is no need to wash hands before eating a food dipped in liquid.
In practice, we wash our hands before eating karpas, but do not recite a blessing, in order to fulfill all opinions: on the one hand, we wash our hands in accordance with the poskim who require it, but on the other hand, we do not recite a berakha because there are those who maintain that nowadays there is no need to wash hands before eating food dipped in liquid (SA 473:6).
If one mistakenly recites a blessing over this hand washing, he is not guilty of a berakha le-vatala (a blessing in vain), since he has acted in accordance with the majority of poskim, including Levush and Gra, who require a berakha when washing hands for a food dipped in liquid. However, the le-khatĥila ruling is not to recite a berakha, because we rule leniently in cases of uncertainty about berakhot.
Furthermore, if one mistakenly recites a berakha over the first hand washing, this does not exempt him from the second hand washing, and he must recite a blessing over it as well. This is because people are not meticulous about keeping their hands clean between the two washings. In addition, the time spent reciting the Hagada constitutes an interruption between the two hand washings, and therefore the Sages ordained washing hands twice at the Seder (see Kaf Ha-ĥayim 473:107; BHL 475:1; Mikra’ei Kodesh ch. 7 n. 8).