The end of last week's Parsha (Chayei Soro) 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, "ViAyleh Toldos Yitzchok" - "And these are the offspring of Yitzchok".
Baal HaTurim explains the connection. "Al Pnei Kol Echov Nafal" - when Yishmael - (the Arabs) will fall, then, "ViAyleh Toldos Yitzchok" - Mashiach Ben David will come from the descendants of Yitzchok.
The fall of Yishmael is a prerequisite for the coming of the Mashiach.