This sheet is part of a series of source sheets related to Mishnayos Yadayim. Other sheets include
A collection of Mishanyos discussing Tumas Yadayim (http://www.sefaria.org/sheets/46080)
Running commentary on Mesechtas Yadayim (http://www.sefaria.org/sheets/47899)
Seforim and Tumas Yadayim (http://www.sefaria.org/sheets/53851)
The Gemara in Chullin identifies this Pasuk as the source for Netillas Yadayim (purifying one's hand by washing them). Although all agree that this rule is a Rabbinic Decree, nonetheless, the Chachomim always looked to find a source or a hint of the rule in the Torah itself.
This Parsha (found in parshas Ki Sisah) describes how when entering the Beis HaMikdash to do the Avodah, the Kohanim would wash their hands and feet. This washing was meant to enhance and recognize the extremely holy nature of the Beis HaMikdash. It was not meant as a purification ritual. Nonetheless, over time, and especially after the Beis Hamikdash was destroyed, the Chachomim relied on this parsha to institute Netillas Yadayim even for Chulin food. The Gemara related a tradition that Shlomo HaMelech himself instituted Netillas Yadayim.
This Mishna sets out one historical source for the Decree of Tumas Yadayim
This Gemara describes the basis and traces the historical stages of the decree of Tumas Yadyaim.
This Gemara sets out many of the dinim and details for Netilas Yadayim.
The RAMBAM provides a brief history of the decree of Tumas Yadayim
The RAMBAM describes the impurity of Sefrei Kodesh and how the Chachomim bolstered their original decree by decreeing that the hands that touch the seforim become a Sheini L'Tumah as well.
The RAMBAM sets out the rule that Tumas Yadayim are always a שני לטומאה (a second degree of Tumah)
This Midrash shows how Netilas Yadayim transformed from a Purity ritual to a Holiness ritual.