1) ONE WHO IS PERFORMING A MITZVAH IS EXEMPT FROM OTHER MITZVOS
QUESTION: The Gemara says that one who is involved in a Mitzvah is exempt from the Mitzvah of Keri'as Shema. This is the source for the general rule, "ha'Osek b'Mitzvah Patur Min ha'Mitzvah" -- "One who is involved in one Mitzvah is exempt from another Mitzvah."
If one is exempt from performing a Mitzvah while involved in the performance of another Mitzvah, then a man who is wearing Tzitzis or Tefilin should be exempt from all other Mitzvos! We know, of course, that this is not so. When exactly does this principle apply? (TOSFOS, Sukah 25a, DH Sheluchei Mitzvah)
(a) TOSFOS answers that only when the second Mitzvah would interrupt one's performance of the first Mitzvah is the person exempt from the second Mitzvah. If one could perform the second Mitzvah without interfering with his performance of the first Mitzvah (such as is the case when wearing Tzitzis or Tefilin), he is not exempt from the second Mitzvah.
The OR ZARU'A questions the answer of Tosfos. It is obvious that one may not stop performing one Mitzvah in order to perform another. Why would we have thought to give precedence to one Mitzvah over another had the verse not taught us otherwise?
We could answer that Tosfos learns from the verse that one who is involved in one Mitzvah is exempt from other Mitzvos even in a case where the opportunity for the second Mitzvah will pass if it is not done right away. One might have thought that in such a situation, one should interrupt the performance of the first Mitzvah and fulfill the second Mitzvah. The verse teaches us that even in such a case, one may not leave the first Mitzvah to perform the second. (M. KORNFELD)
(b) The RASHBA in the name of RAV HAI GA'ON, the MAGID MISHNEH (Hilchos Sukah 6:4) in the name of the GE'ONIM, and the OR ZARU'A (Hilchos Sukah) explain that as long as a person is involved in preparing to fulfill a Mitzvah, such as when he is traveling in order to perform a Mitzvah, he is not obligated by the Torah to perform other Mitzvos even if they do not distract him from the first Mitzvah. Hash-m does not expect us to do two things at once.
Accordingly, we may suggest that with regard to Tzitzis and Tefilin, one has already done what was necessary in order to prepare to fulfill the Mitzvah. He has done everything necessary for the fulfillment of the Mitzvah, and he is now in the process of passively fulfilling the Mitzvah, and not in the process of preparing to fulfill the Mitzvah. The exemption from other Mitzvos applies only when one has not yet fulfilled the first Mitzvah and is involved in the preparatory stages of fulfilling the Mitzvah.
(c) The RAN in Sukah (25a) suggests a compromise. He agrees with the Rashba that one is exempt from the second Mitzvah even if its performance does not distract him from the first Mitzvah. However, if there is a way to fulfill the second Mitzvah while still performing the first Mitzvah in its normal manner, then one is not exempt from the second Mitzvah (as the Ran writes, "why not fulfill a Mitzvah if nothing is lost while doing so?"). Only if one must change his normal way of performing the first Mitzvah in order to fulfill the second Mitzvah is he exempt from the second Mitzvah.
(It could be, according to the Ran, that the obligation to do the second Mitzvah does not stem from the normal obligation to perform Mitzvos, but rather from the requirement that one avoid disgracing a Mitzvah. Technically, he may be exempt since he is involved in another Mitzvah, but in practice -- since the second Mitzvah could be performed without making any change from one's normal way of performing the first Mitzvah -- it would be disgraceful to the second Mitzvah not to perform it. -M. KORNFELD)
HALACHAH: The REMA (OC 38:8) cites the opinion of the Ran as the Halachah. When there is a way to fulfill the second Mitzvah while still performing the first Mitzvah in its normal manner, one is not exempt from the second Mitzvah. Otherwise, he is exempt.
2) RECITING THE SHEMA AT NIGHT LIKE BEIS SHAMAI
QUESTION: Beis Shamai and Beis Hillel argue in the Mishnah (10b) with regard to how one should recite the Shema. Beis Shamai requires one to recline when reciting it at night, and to stand when reciting it by day. Beis Hillel says that one may recite the Shema in whatever position he wants. The Gemara (11a) qualifies this and says that just as Beis Shamai says that one who eats in a Sukah in the manner of Beis Hillel does not fulfill his obligation, so, too, according to Beis Hillel, one who recites the Shema at night while reclining (like Beis Shamai) does not fulfill his obligation.
What is the comparison between the Mitzvos of Sukah and Keri'as Shema? In the case of the Sukah, Beis Shamai's opinion is that one does not fulfill his obligation at all if he sits in the Sukah in the manner of Beis Hillel. Regarding Keri'as Shema, Beis Hillel himself rules that one may recite the Shema in whatever position he wants. Why, then, does the Gemara say that according to Beis Hillel a person does not fulfill his obligation if recites the Shema at night while reclining?
(a) TOSFOS (DH Tani) explains that Beis Hillel agrees that l'Chatchilah one should not recline and recite the Shema. TOSFOS HA'ROSH explains that the reason for this is that others may mistakenly think he is reclining because the Halachah is like Beis Shamai, and they will assume that one is required to recline. This will result in the possibility that when they find themselves in a situation in which they cannot recline, they will not recite the Shema at all. Now that it is clear that at least l'Chatchilah one should not recite Shema while reclining, we may derive from the ruling regarding the Sukah that even b'Di'eved one does not fulfill the Mitzvah.
(b) TALMIDEI RABEINU YONAH answer that if one reclines and recites the Shema, it appears as though he is rebelling against Beis Hillel. For this reason, one should not read Shema while reclining if the Halachah is like Beis Hillel. Now that it is clear that at least l'Chatchilah one cannot recite Shema reclining, we may derive from the ruling regarding the Sukah that even b'Di'eved one does not fulfill the Mitzvah.
HALACHAH: The Halachah is like Beis Hillel (SHULCHAN ARUCH OC 63:1), and one may recite the Shema in whatever position he wants (except for certain disrespectful positions as described later on 14b). If one specifically stands up from a sitting position in order to say the Shema in the morning, or one sits down at night, he is called a "sinner." Nevertheless, he does not have to repeat the Shema (Shulchan Aruch OC 63:2, Mishnah Berurah 63:5).
3) THE BLESSINGS OVER LEARNING TORAH
QUESTION: The Gemara says that if one did not recite Birchos ha'Torah (the blessings over learning Torah) before he started to pray in the morning, he does not need to recite them later. He fulfills his obligation to recite those blessings through the recitation of the blessing "Ahavah Rabah." This implies that the recitation of Birchos ha'Torah (or their substitute, "Ahavah Rabah") in the morning covers one's learning for the entire day.
TOSFOS (DH she'Kevar Niftar) points out an apparent contradiction in the Halachos of blessings. Before eating in a Sukah, one must recite a blessing. If he leaves the Sukah to go about his business, he must recite the blessing again when he returns to eat in the Sukah. Regarding Birchos ha'Torah, however, once one has recited the blessing in the morning, he does not need to repeat the blessing during the day even if he interrupts his Torah study to engage in business or other pursuits. What is the difference between the blessing for learning Torah and the blessing for eating in a Sukah?
(a) TOSFOS explains that the Mitzvah to study Torah applies during every moment of the day (see Insights to Berachos 35:3). Therefore, involvement in other tasks does not mean a cessation of one's Torah study. The Mitzvah of Sukah, on the other hand, applies only while eating. Therefore, if one leaves the Sukah to go about his business, he must recite a new blessing before eating in the Sukah a second time.
This is supported by the Tosefta (Avodah Zarah 1:3; see also Menachos 99b) that says: Rebbi Yehoshua was asked, "May a man teach his son Greek wisdom?" He responded, "He may do so, but only during a time which is neither day nor night, for during the entire day and the entire night one is obligated to study the Torah and there is no free time in which to engage in the teaching or practice of Greek wisdom. As the prophet says, 'You shall ponder the Torah day and night!'" (Yehoshua 1:8).
(b) The ROSH (1:13) resolves the contradiction between the two blessings in a slightly different manner. According to the Rosh, only people who are fully immersed in the study of Torah are justified in refraining from reciting a new blessing after a pause in their Torah study. Even when such people tend to their everyday affairs, they are eager to finish their chores and return to the study of Torah. Because their minds are never distracted from the study of Torah, their earlier blessing is still valid when they return to study Torah.
The Rosh teaches us that a true student of the Torah finds all worldly pursuits to be no more than distractions that temporarily interrupt his Torah study. The Rosh's source is undoubtedly the Gemara's teaching (Berachos 35b) that "the earlier generations considered Torah study to be their fixed pursuit and earning a livelihood to be a temporary diversion, and they therefore succeeded in both" (see also Yoma 19b, "Make the study of Torah a fixed pursuit, not a temporary diversion").