What contrast is the Pasuk striking here between Yefes and Shem?
Rashi #1: Although HaSh-m will extend the borders of Yefes, He will dwell exclusively in the tents of Shem (The Mishkan and the Beis-ha'Mikdash). 1
Rashi #2: Even though He will "beautify" Yefes
Gur Aryeh: Why does Rashi insert the phrase "even though" into the explanation of the verse? The difficulty here stems from the verses beginning with Shem (9:26), continuing to Yefes, and then returning to Shem. Rashi therefore explains that the verse is expressing one idea.
Why does the Torah repeat the phrase, "And he will be a slave to them"?
Rashi: Even when Yisrael are in exile, they will acquire sons of Kena'an as slaves.
Seforno: They will be slaves to Bnei Yisrael even before the Beis ha'Mikdash is built. 1
Targum Yonasan: The previous Pasuk refers to Shem personally. This Pasuk refers to his offspring and to the converts of Yefes. 2
Ramban, Ibn Ezra: He will be a slave to Shem and Yefes.
Since the previous Pasuk (9:25) taught that Kena'an is a slave to the entire world, what does the phrase "he will be a slave to them" add?
Ramban: Through calling Kena'an a slave of Shem twice (and Yefes only once), he was hinting that he (Shem and not Yefes) would inherit Kena'an's land and all that he owned. 1
Whatever a slave owns, belongs to his master.
Why does the Torah deem it important to tell us about the episode of Kena'an?
Ramban: It teaches why Kena'an became an everlasting Eved, and how Avraham merited to inherit his land.
Why does the Torah deem it important to tell us about Noach's drunkenness?
Ramban: It teaches us the dangers of drinking. We find that Noach the Tzadik, who saved the whole world with his righteousness, fell prey to its allure, and it led to his disgrace and to the curse of some of his offspring.
רש"י: אף על פי שיפת אלוקים ליפת וכו': מנין לפרש את הפסוק בצורה של 'אע"פ'?
גור אריה: קשה למה הפסוק התחיל בשם, המשיך ביפת וחזר לשם? לכן פירש רש"י שכל הפסוק אחד- אע"פ שיפת אלוקים ליפת וכו'.