בראשית כה:כא פירוש: רש״י, רשב״ם, ספורנו ואור החיים

וַיֶּעְתַּר AND ISAAC ENTREATED —He prayed much and urgently.

ויעתר, an expression denoting a lengthy prayer, as in Ezekiel 35,13 העתרתם עלי דבריכם, “you multiplied your words against Me.”

לנכח אשתו, even though he had been given an assurance from G’d that he would produce seed, he prayed to G’d that the mother of this child or children should be someone who was meritorious, someone of the calibre of Rivkah who was present and standing opposite him..