The Slonimer chassid, Reb Mordechai (Motke) Leider zt'l of Teveria, was once very ill as a young man; people thought he would die. After miraculously recovering, he came to the Slonimer beis medresh in Teveria. He announced, "Yesterday, I almost did the kuntz" (trick, implying that he almost died and went up to heaven. He was telling that this would have been better for him because then he wouldn’t have the tests of this world).
Another Slonimer chassid, Reb Elazar Katz zt'l, replied, "What did you say? That you almost made 'the kuntz'? How would you survive up there in heaven without a לא תתורו (the mitzvah to be cautious with one's eyes)?"
It states (6:8) 'ה בעיני חן מצא ונח, "Noach found favor in Hashem's eyes." The Beis Avraham zt'l taught that Noach found chen 'ה בעיני because he was cautious with his eyes.
The Torah (9:23) tells us that Shem and Yefes covered their father, Noach. For this good deed, Yefes was rewarded that his descendants were brought to burial, and Shem was rewarded with the mitzvah of tzitzis.
When Shem and Yefes went to cover Noach, they walked backward so they wouldn't see Noach unclothed. While covering him, they had to turn towards their father, but they were cautious to turn their faces away.
Rashi (9:23) says that this is the reason it states אחרונית, backward, twice in this pasuk (see footnote). One refers to when they entered the room, and the other אחרונית is when they covered their father. Their bodies faced Noach to cover him, but they turned their faces away. This is how cautious they were to guard their eyes and not to disgrace their father.
The Alshich HaKadosh asks, why didn't they simply close their eyes? The Alshich answers that even facing an ervah creates a p'gam, a blemish, on one's soul.
In contrast, the Torah (9:24) tells us, חם וירא אביו ערות את כנען אבי, "Cham, the father of Canaan saw his father's ervah." Chazal (Sanhedrin 70) reveal other terrible sins that Cham did to his father, but from the literal words of the pasuk, it seems that Cham's sin was that he saw his father's ervah. The Beis Yisrael zt'l said we should learn from this the severity of not guarding one's eyes. For that sin alone, Cham deserved all the curses he received.
