The Gemara in Shabbos (156a) cites a Machlokes Amora'im regarding whether
"Yesh Mazal l'Yisrael" (does Yisrael have Mazal) or not. Rebbi Yochanan says
"Ein Mazal l'Yisrael," because Hashem took Avraham Avinu above the Mazalos.
RASHI there explains that even according to this opinion, a Jew can alter
his Mazal through Tefilah and through personal merit.
(a) Rebbi Yakov might not mean that it is impossible for a person to receive
reward in this world, as is clear from TOSFOS (DH Masnisin) who explains
that Rebbi Yakov agrees that a Rasha is given reward in this world so that
he will not receive reward in Olam ha'Ba, the World to Come. Rebbi Yakov
means, rather, simply that the reward in the World to Come is much more
valuable than its manifestation in this world, if it would be given in this
world. Therefore, it is not beneficial for Hashem to give the Tzadik reward
in this world, and in order to give the Tzadik the best form of reward,
Hashem saves it for the World to Come.
The Rabanan, who argue, maintain that it can indeed be more beneficial for a
Tzadik to receive reward in this world, because when he has tranquility and
comfort he has the ability to perform more Mitzvos and thereby acquire more
reward in the World to Come, which he would not have been able to do had he
been suffering from Yisurin in this world.
It is possible, then, that Rebbi Yakov and the Rabanan are both correct.
Certain Tzadikim can only serve Hashem with all of their potential if they
have tranquility and comfort, and for such Tzadikim it is better to receive
reward in this world. Other Tzadikim are able to serve Hashem even through
suffering and material limitations, and for these Tzadikim it is better to
leave the reward for the World to Come. With regard to the first type of
Tzadik, all agree that "Ein Mazal l'Yisrael," and that it is possible for
them to receive benefits in this world due to their merits.
In addition, it is possible that Rebbi Yakov agrees that if a Tzadik
beseeches Hashem through *Tefilah* to receive a certain benefit (because he
thinks that it is necessary for his Avodas Hashem), then Hashem will answer
his Tefilah and give him what he requests because of his merits. He does not
argue with the Beraisa that we recite every morning after Birkos ha'Torah
that says that "Iyun Tefilah" and "Hashkamas Beis ha'Midrash" bear rewards
in this world.
RASHI (DH Masnisin) seems to disagree with Tosfos and learns that even
according to the Rabanan, a Tzadik may suffer in this world in order not to
receive punishment in the World to Come, and any reward that a person
receives in this world diminishes his reward in the World to Come. (See
Tosfos DH Masnisin.) In what way, then, do the Rabanan say that a person
*does* receive reward in this world without diminishing his reward in the
World to Come?
Perhaps Rashi maintains that Rebbi Yakov and the Rabanan argue only with
regard to Mitzvos whose reward is written explicitly in the Torah, like
Kibud Av v'Em and Shilu'ach ha'Ken. The Rabanan hold that the reward written
in the Torah is in addition to the reward that is reserved for the World to
Come, and it in no way affects his future reward, while Rebbi Yakov argues
and says that the reward of these Mitzvos, too, is only given in the World
(b) RAV ELCHANAN WASSERMAN in KOVETZ HE'OROS (Bi'ur Agados Al Derech
ha'Peshat 2:4-5) cites the TESHUVAS HA'RASHBA who explains that the
blessings in the Torah apply to the nation as a whole, and not to each
individual Jew. Rav Elchanan explains that even if there is no reward for
Mitzvos in this world, Hashem certainly rewards the people when the nation
as a whole observes His Mitzvos, without that reward detracting from their
reward in the World to Come, since the community as a whole is not judged in
the World to Come. (See also MAHARSHA.) (Concerning the question of "Yesh
Mazal l'Yisrael," see Insights to Moed Katan 28:3.)