Exodus 30:19

And they shall take from it for a cleansing ablution. And Aharon and his sons shall sanctify their hands and their feet with its water;

AND AARON AND HIS SONS SHALL WASH THEIR HANDS AND THEIR FEET THEREAT. This washing was out of reverence for Him Who is on high, for whoever approaches the King’s table to serve, or to touch the portion of the king’s food, and of the wine which he drinks, washes his hands, because “hands are busy” [touching unclean things automatically]. In addition He prescribed here the washing of feet because the priests performed the Service barefooted, and there are some people who have impurities and dirt on their feet.
By way of the Truth, [the mystic teachings of the Cabala], these parts of the body had to be washed because the extremities of the person’s body are his hands and feet, for when the hands are upraised they are higher than the rest of the body, and the feet are the lowest point. They allude in the human form to the Ten Emanations, with the whole body between them, just as the Rabbis have said in Sefer Yetzirah: “He made a covenant with him [i.e., Abraham] between the ten fingers of his hands and the ten fingers of his feet, with the protrusive part of the tongue and with the protrusive part of the nakedness.” Therefore the ministers of the One on High were commanded to wash their hands and feet, this washing being for the sake of holiness, as Onkelos translated here, l’rochtzah (to wash): l’kidush (to sanctify). (washing) literally. It is on the basis of the idea of this commandment that our Rabbis have instituted the washing of hands before prayer, in order that one should direct one’s thoughts to this matter, just as in the uplifting of hands by the priests when blessing the people.
It is the washing which is the essence of the commandment, but He commanded [the making of] the laver only in order that the water should be ready in it. Thus the absence of the laver does not invalidate the washing, neither is there any duty [to do the washing specifically from the laver]; thus on the Day of Atonement the High Priest washed his hands and feet from a golden jug which they made in his honor. However, what we do learn from the laver [that the Torah mentions], is that the washing [of the hands and feet by the priests] must be performed from a vessel.