We wash our hands, Netilat Yadayim, for a multitude of reasons. A few examples include washing when we wake up in the morning, washing before we eat bread, and washing before we eat Karpas at the Pesach Seder. The common theme of all the aforementioned situations is not washing because of our personal hygiene, but rather washing because of our spiritual cleanliness.
In Halachah, there is a concept of Tum’ah and a concept of Tahorah. Tum’ah is when we are spiritually unclean, and Tahorah is when we are spiritually pure. There are six different levels of Tum’ah. The highest level is called Avi Avot HaTum’ah, which is a dead body or a metal vessel that touches a dead body, and the second level is Av HaTum’ah, which can be, for example, a person who comes in contact with a dead body or a Metzora, a person with leprosy. For a person or a person’s vessel to become Tahor again after coming in contact with the first level of Tum’ah, the person or the vessel would need to be sprinkled with the ashes of the Parah Adumah, the red heifer.
Furthermore, a person, vessel, food, or water that touches any of the Avei HaTum’ot would become a Rishon LeTum’ah, the third level of Tum’ah. The fourth level of Tum’ah is Sheini LeTum’ah, consisting of foods or liquids that touch a Rishon LeTum’ah. And, according to the Gemara (Shabbat 13b), hands that are not rinsed are categorized as Sheini LeTum’ah.
Finally, there are the fifth and the sixth categories of Tum’ah, which are pertinent only to Kohanim. The fifth level is called Shelishi LeTum’ah: Terumah (bread, oil, and wine) or Kodshim (meat), special categories of food that are designated for the Kohanim to eat, which touch a Sheini LeTum’ah. And the sixth level, Revi’i LeTum’ah, are Kodshim that touch a Shelishi LeTum’ah. When the Beit HaMikdash was standing, before a Kohein would be allowed to eat his Terumah or Kodshim, he would need to wash his hands because of Setam Yadayim, the concern that his hands might have become impure by mistake. Today, we wash our hands for bread because of a Gezeirah made by the Rabbanan, which required Bnei Yisrael to wash their hands before eating bread to ensure that the Kohanim wouldn’t forget to wash for their Terumah bread when the time would come.
The Gemara in Pesachim (115a) discusses the significance of washing one’s hands for Karpas. Rabi Elazar quotes Rav Oshaya who says that one must wash one’s hands before eating food that is dipped in liquid. This requirement is because of the Chachamim’s concern that fruit or vegetables can become Tum’ah from contact with impure hands. On Pesach we eat Karpas dipped in salt water. During the times of the Beit HaMikdash when the Bnei Yisrael were required to have the Korban Pesach, not washing hands for Karpas would lead to complications. Hands are Sheini LeTum’ah because of Setam Yadayim; therefore, hands would make the Karpas Tamei, and eating the impure Karpas would make the person Tamei. This situation was very undesirable because Jews would need to immerse in a Mikvah to become pure again, and would risk not being able to eat the Korban Pesach.
The Shulchan Aruch (Orach Chaim 473:6) teaches that before we eat the Karpas, we are required to wash our hands. It also adds, though, that we don’t recite a Berachah on the washing. The Taz (ad. loc. s.v. VeLo Yevareich Al HaNetilah) says that based on the fact that we wash for Karpas on Pesach, we should be washing our hands for fruits and vegetables year-round. However, since this is no longer the common practice, we do not recite a Berachah when washing for Karpas at the Seder. Ideally, though, one should wash and make a Berachah before eating fruits and vegetables year-round. Taz’s position is unique, however, as the Tur and Rabbi Eliezer Maimitz both rule that we do not wash our hands year-round before eating wet fruits and vegetables, and while we do wash on the night of Pesach, we do not make a Berachah.
But why is the Seder night different than all other nights? According to most customs, we don’t wash our hands year-round for wet fruits and vegetable, but on this night we do! The answer is simple, identical to many others answers on the Seder night: to prompt the children to ask questions. Asking questions is an important part of the spiritual growth for all Jews, and it is especially important for children. On a night when we relive the experiences to teach the Mesorah, the tradition, of Yetzi’at Mitzrayim, we try to spark the act of questioning early on in the night by doing Mitzvot out of the ordinary.