The end of last week's Parsha finishes with the words, "Al Pnei Kol Echov Nafal" - "Over all his brothers he [Yishmael] shall fall".
This week's Parsha starts with the words, " ViEileh Toldos Yitzchak" - "And these are the offspring of Yitzchak".
Baal HaTurim explains the connection. "Al Pnei Kol Echov Nafal" - when Yishmael - [the Arabs] will fall, then, "ViAyleh Toldos Yitzchak" - Mashiach Ben David will come from the descendants of Yitzchak.
The fall of Yishmael is a prerequisite for the coming of the Mashiach.