When a Jew gazes at an immodestly dressed woman, or looks at an erotic image on the Internet, he blemishes his holiness. Just as a radio stops working when you pull out its plug from the electric socket, when a person looks at a forbidden image, he or she shortcircuits the connection to G-d.
In the Torah reading fo Shabbat, Yehuda goes astray after Tamar, who has disguised herself as a prostitute. Living up to his agreement with her, he sends a messenger with her payment. When the messenger can't find her, he asks the people of the place, "Where is the prostitute, the one at the crossroads by the road?" (Bereshit, 38:21)
The Kabbalist, Rabbi Leon Levi, explains that the word for prostitute, "kedasha," can be read as "kedusha" meaning holiness.The word for "at the crossroads" is "b'anayim," which also means "in the eyes."
איה הקדושה הוא בעינים
According to the inner understanding of the verse, the Torah is teaching: "Where is holiness?" and it answers, "In the eyes."