What is the connection between this Pasuk and the previous ones?
Rashi: When Hashem scattered the Dor Haflagah, He did not destroy them, because Hashem's portion - His people, Ya'akov - was contained among them and was destined to come out from them. 1
Ramban (on Pasuk 7, citing the Ibn Ezra): This relates the uniqueness of Yisrael, "Ha la'Shem Tigm'lu Zos!?" - 'How could you do this to Hashem who raised you to such a high level, which He did not do to any other nation!?' "Am Naval ve'Lo Chacham" - 'In your foolishness, you fell from that level!'
Rosh (on Pasuk 8): This explains why Hashem started [arranging] the inheritance of Yisrael, for He took them for His portion.
Why does the Torah mention specifically Ya'akov?
Rashi #1: Because he was the third of the Avos who possessed a triple merit - that of his grandfather (Avraham), that of his father (Yitzchak) and his own - like a rope of three strands. 1
Rashi #2: All Ya'akov's sons are Hashem's portion
What are the implications of "Ya'akov Chevel Nachalaso"?
Rashi: Refer to 32:9:2:1.
Seforno: It implies that Ya'akov and his sons (and sons' sons) are servants of Hashem - but if a pious man is to be found among the other nations, his status is not passed down to his descendants.
Targum Yonasan: When Yisrael fell to Hashem's portion, 1 the Angel Micha'el announced "Ki Cheilek Hashem Amo!" and the Angel Gavriel opened his mouth in praise and declared "Ya'akov Chevel Nachalaso!"
Hadar Zekenim, Rosh (on Pasuk 8): Yisrael is Hashem's portion.