Halakhah for Zevachim 38:3

From the roots of the commandment is the fixed foundation that we have said [that it is] to aggrandize the glory of the [Temple] and all of the [activities] that are done there. And therefore it is fitting to clean the hands, which are the [things] that are involved in the work at all times when the priests are touching the contents of the [Temple]. And from this root, they, may their memory be blessed, said (Zevachim 19b) that the priest does not need to sanctify his hands between one service and [another] service, but rather once during the morning, and he may [then] serve the whole day and the whole night - and that is when he does not sleep and does not urinate and does not remove his mind. It appears from all of this that the intention of the washing at the beginning is only for the aggrandizement of the glory of the [Temple], since even if he was pure and clean from the beginning of his arrival there, he [still] needs to wash. And once he has started the service, he does not need to wash again between one service and [another] service, except for on Yom Kippur, due to the stringency of the day. [This is all] since we hold and see in our hearts all of the business of the service of the [Temple] as pure, clean and holy.

And so [too,] that which they, may their memory be blessed, said (Zevachim 21b), [about] how much water needs to be in the basin - [that it is] no less than water that is fit for the [washing] of four people - as it is is stated, "And let Aharon and his sons wash their hands and their feet." And they were Aharon and Elazar and Itamar, and Pinchas was with them. And that all water is fit for sanctification - whether the water from a spring or the water of a pool (mikveh) - and they are disqualified by [passing the night]. And how is the commandment of the sanctification (Zevachim 19b) - that he places his right hand on his right foot and his left hand on his left foot and washes standing up and not sitting. As the sanctification of the hands and feet is included in the service, and all of the services of the Temple are [done while] standing up - as it is stated (Deuteronomy 18:5), "to stand and to serve." And all of this is for the loftiness of the [Temple]. And the rest of its details are elucidated in the second chapter of Zevachim.