רבינו בחיי — ויעתר יצחק לה' לנכח אשתו כי עקרה היא

Q — Why does the pasuk open with Yitzchak's prayer and then mention Rivkah's barrenness — shouldn't it follow chronology, first establishing the barrenness and only then describing the response to it?

A — Rabbeinu Bachya reads the word-order as a chiddush: the tefillah is the עיקר, the barrenness is its טפל. "אין הכונה שתהיה העקרות סבת התפלה שא"כ הסבה עיקר והתפלה טפל לה, אבל הכונה לשון הכתוב כי התפלה סבת העקרות" — the akarut was not the cause of the tefillah; the tefillah was the cause of the akarut. Hashem made Rivkah barren specifically in order to elicit the prayers of the tzaddikim — which is why the same pattern recurs in three of the four Imahot. The chiddush: nature can be re-engineered backwards from tefillah. The world is structured so that the desired prayer of a tzaddik is the underlying cause and the apparent suffering is merely its conduit. The pasuk's syntax encodes this reversal directly.