One should know that the principle aspect of a Jew's holiness and purity is in sanctifying his eyes. The Torah emphasizes this in the verse regarding Yehuda by asking, "Where is the k'deisha?" While the word k'deisha has the meaning "harlot," it can also be read in its meaning of "holiness," so that we read, "Where is the holiness?" And the answer is "b'Anayim," which means that the harlot was in the place called Anayim, but also that the holiness of a Jew is in the Anayim - the eyes (Bereshit, 38:21).