Why does the Torah write "va'Ye'tar," and not 'va'Yispalel"?
Rashi and Rashbam: "Va'Yetar" denotes, not just Tefilah, but intense, consistent prayer.
Moshav Zekenim, from Sotah 14a: Tefilos of Tzadikim are called Eter (a pitchfork), for just like an Eter moves grain from place to another, their Tefilos 'move' HaSh-m from the Midah to anger to the Midah of mercy. 1
The Gemara (Yevamos 64a) teaches that Yitzchak's prayer is called an 'Eser' (Ayin-Sav-Resh), because the prayers of the righteous turn HaSh-m's trait of anger to that of mercy, just as an 'Eser' (a pitchfork) turns over the grain. What is a deeper meaning of the analogy?
Maharal (Chidushei Agados Vol. 1, p. 142, to Yevamos 64a): The prayers of most people, even if accepted, cannot overturn Midas ha'Din into Midas ha'Rachamim. Only the righteous can reach with their prayers to a place of absolute mercy. 1
We may explain that even Midas ha'Din stems from HaSh-m's desire to bestow good. The righteous are the ones who discover this Midah, through their prayers. Perhaps this is what is meant by Midas ha'Din turning over into Rachamim. (EK)
Why does the Torah juxtapose "va'Ye'tar Yitzchak La'Sh-m... Ki Akarah Hi" next to "Achos Lavan ha'Arami..." (25:20)?
Oznayim la'Torah (to 25:20). To teach us that Lavan ha'Rasha's Tefilah (24:60) did not bear fruit, and that Rivkah remained barren until Yitzchak prayed for her.
Ha'amek Davar: Since she was from Aram, and Lavan's sister, her children should have had a cruel nature. Therefore HaSh-m made her barren, so she would give birth miraculously, and her children will not have this nature.
What are the implications of the fact that Yitzchak and Rivkah had to pray for children?
Oznayim la'Torah: It is in praise of Yitzchak and Rivkah, as Chazal have said, 'Fruit-trees require nurturing, whereas barren trees grow by themselves.' Likewise, Tzadikim need to pray for children, whereas Resha'im multiply automatically. 1
Malbim: The Imahos [except for Leah] were barren, for nature does not produce a Kadosh child. Through Tefilah, HaSh-m puts in a G-dly Neshamah.
Oznayim la'Torah: And the fact that they had to pray for children was a sign that they were Tzadikim and that HaSh-m longed for their Tefilos.
The Gemara (Yevamos 64a) writes that the forefathers were [initially] barren, because HaSh-m desires the prayers of the righteous. Why specifically those of the righteous?
Maharal (Chidushei Agados Vol. 1, p. 141, to Yevamos 64a): Prayer is the connection of a created being to his Prime Cause (HaSh-m) - by acknowledging his dependence upon Him. 1 The forefathers are the foundation of the world; 2 by virtue of their connecting with HaSh-m (through their prayer), the entire world is connected to Him. HaSh-m 'desires' this, for to be a bestower of goodness requires that there be a recipient, who will recognize the giver. The righteous are the ones who humble themselves before HaSh-m in this way. 3
How did Yitzchak know that Rivkah was barren? Perhaps he was barren, or perhaps both of them!
Riva, Moshav Zekenim #1: The verse "Seed will be called to you through Yitzchak" (21:12) proves that he is not barren.
Moshav Zekenim #2: "[Akarah] Hi" is written like "Hu," to teach this. 3
Yayin ha'Tov says that this is a mistake; it should say '20.'
Peirush Yonasan: He too was destined to be barren, and his Tefilah overturned the decree.
In 200 places, the Torah writes "Hi" like Hu, and in only 11 places with a Yud! Perhaps all 200 should be expounded, like every "Es" is expounded (Pesachim 22b). (PF)
QUESTIONS ON RASHI
Rashi writes: "Va'Ye'tar - [Yitzchak] increased and entreated constantly (Hiftzir) in his prayers." Why does Rashi add the word 'Hiftzir"?
Gur Aryeh: "Va'Ye'tar" does not mean generic increase, but rather increase by pressing constantly.
Rashi writes: "'Va'Ye'aser Lo' - HaSh-m received his entreaty, and was appeased and convinced by him." Why does Rashi use all of these terms?
Gur Aryeh: We cannot explain that HaSh-m was 'pressured' [for HaSh-m accedes to requests only according to His will]. Rashi defines the 'pressure' to mean 'appeasement until the prayer is accepted.' Rashi then adds the term 'convinced,' for there was no anger that would need to be 'appeased.' But Rashi does not use the term 'convinced' alone, as that would imply it was against His will.
Rashi writes: "Every instance of the root 'Eter' (Ayin- Tav-Resh) means pressing and increase." Why does Rashi add this?
Gur Aryeh: We may have thought that it only means this in our verse (for lack of a better explanation). Rashi adds that this is what it means in other cases as well.
Rashi writes: "So too in the verse, 'Na'ataros (thick, heavy) are the kisses of an enemy;' they seem heavy and are a burden." Does an enemy give many kisses?
Gur Aryeh: As Rashi writes, 'they seem to be many;' i.e. they are a burden to the recipient and are superfluous.
Rashi writes that Yitzchak and Rivkah both prayed simultaneously, in opposite corners. Why did HaSh-m answer Yitzchak (first)?
Rashi (from Yevamos 64a): Because 'one cannot compare the Tefilah of a Tzadik ben Rasha to that of a Tzadik ben Tzadik.' 1
Targum Yonasan: In fact, it was Yitzchak alone who went to Har ha'Moriyah 2 (where his father had bound him), on behalf of his wife who had been barren for twenty years.
Seforno, based on Sechel Tov: HaSh-m had promised that Yitzchak 3 would bear children - "Ki v'Yitzchak Yikarei Lecha Zara" (21:12). [Only] he prayed, that should be fulfilled through this Tzadekes!
Since in the realm of Tefilah, Zechus Avos plays a major role. When Aba Chilkiyah and his wife prayed for rain, HaSh-m answered her prayers first. He explained that this was because she would give food to a poor man, while he would only give him money with which to buy food. Aba Chilkiyah's grandfather was the Tzadik Choni ha'Me'agel! Oznayim la'Torah - (a) Perhaps his wife's ancestors were equally righteous. (b) There, they were praying for rain, so HaSh-m gives precedence to those who satiate the poor - Midah K'Neged Midah. Here, they were praying for children, and the chances of a Tzadik ben Tzadik raising righteous children are higher than those of a Tzadik ben Rasha. See his third answer.
Oznayim la'Torah: Since (a) It is the gateway to heaven and (b) It was the location where the Akeidah took place and where HaSh-m had told his father "Harbah Arbeh Es Zar'acha" - about which the Midrash Rabah comments 'Rabos l'Av, Rabos l'Ben!
Yitzchak was promised to have children, but not necessarily from Rivkah. (This is not explicit in the verses, but so the Malbim (22:9) explained. - PF) .
Rashi writes: "'Opposite his wife' - He would stand in this corner and pray, and she would stand in that corner and pray." Why specifically in a corner?
Gur Aryeh: The word "l'Nochach" (towards) implies that each faced the other. Usually, while praying, one seeks out his own place, where he will not be distracted by his fellow's prayers. Compare with the story of Aba Chilkiya (Ta'anis 23b).
Rashi writes: "One cannot compare the Tefilah of a Tzadik ben Rasha to that of a Tzadik ben Tzadik" (based on Yevamos 64a). Why are they different?
Kli Yakar (to 25:19), Ohr ha'Chayim (to 25:19): For a Tzadik ben Tzadik, his father's merit also helps his Tefilah to be answered.
Ner Uziel (p. 154-158, citing the Kotzker Rav): The sin of Etz ha'Da'as caused evil to be mixed with good. To rectify this and bring Mashi'ach, they must be polarized. We find that Avraham had a totally righteous son, and also Yishmael. His son Yitzchak prayed for the same to occur with his children. Rivkah, a Bas Rasha, lived with utter Resha'im, and abhorred the idea of having a totally evil son. She prayed that the good and evil be mixed in the children. HaSh-m wanted polarization, therefore he accepted Yitzchak's Tefilah. 1
Ner Uziel: This is why the Taz (OC 53:3, based on the Rosh) prefers a Shali'ach Tzibur from a lowly family. There is no general rule that a Tzadik ben Tzadik's Tefilah is preferred. (I think that the Taz holds that the Rosh holds that the attribute of a Ba'al Teshuvah over a total Tzadik (Sanhedrin 99a) overrides the preference for a Tzadik ben Tzadik's Tefilah! - PF)