1) HALACHAH: THE LATEST TIME FOR RECITING THE SHEMA
OPINIONS: Three Tana'im argue with regard to the latest time for saying the Shema at night. Rebbi Eliezer says that one may say the Shema only until the fourth hour of the night. The Chachamim say that one may say the Shema only until midnight (Chatzos). Raban Gamliel says that one may say the Shema until dawn. What is the Halachah?
(a) The ROSH and the TUR (OC 235) rule that one may say the Shema until dawn, l'Chatchilah, like Raban Gamliel (as our Sugya concludes).
(b) The RAMBAM (Hilchos Keri'as Shema 1:9) rules that, l'Chatchilah, one should say the Shema before midnight. If one delayed saying the Shema past midnight, one may fulfill his obligation until dawn. The Rambam seems to be ruling like the Chachamim l'Chatchilah, and like Raban Gamliel b'Di'eved. The Gemara, though, explicitly says that the Halachah is like Raban Gamliel. Why, then, does the Rambam rule like the Chachamim?
1. The BEIS YOSEF (OC 235) explains that the Rambam rules like the Chachamim because the Gemara points out that when a single Chacham argues with several Chachamim, the Halachah is like the majority. We therefore follow the opinion of the Chachamim because they are the majority.
2. The BACH says that the Rambam understands the Gemara like TALMIDEI RABEINU YONAH. He explains that the Chachamim maintain that a decree was enacted in order to prevent someone from delaying the recitation of Keri'as Shema until after midnight (which might cause him to neglect reciting it altogether). The decree states that one who recites the Shema after midnight does not fulfill his obligation, even b'Di'eved. Raban Gamliel agrees that l'Chatchilah one must recite the Shema before midnight, but he argues that b'Di'eved one may recite the Shema after midnight. The Rambam rules like Raban Gamliel. (It is not clear how Talmidei Rabeinu Yonah's understanding of the Chachamim can be reconciled with our Sugya. The Bach suggests a possible answer.)
3. The SHENOS ELIYAHU, cited by the BI'UR HALACHAH (OC 235), explains that the Chachamim and Raban Gamliel agree with each other. Raban Gamliel is explaining the opinion of the Chachamim. He is asserting that when the Chachamim said that one may say the Shema until midnight, they meant that l'Chatchilah one must say it before midnight. B'Di'eved, one may say the Shema until dawn. Both the Chachamim and Raban Gamliel meant to argue with Rebbi Eliezer.
HALACHAH: The SHULCHAN ARUCH (OC 235:3) rules that l'Chatchilah one should say the Shema before midnight, and b'Di'eved one may say the Shema until dawn. However, even according to those who rule that one may say the Shema l'Chatchilah until dawn (see (a) above), that is only if one does not intend to eat or sleep before he says the Shema. If one intends to eat or sleep, he must say the Shema before midnight (as the Beraisa on 4b states).
Regarding saying the Shema after dawn and before sunrise, the Halachach follows the ruling of the Talmidei Rabeinu Yonah. If one intentionally -- or due to negligence -- delayed saying the Shema until after dawn, he may not fulfill his obligation by saying the Shema before sunrise. If the delay was due to circumstances beyond his control, then he may recite the Shema before sunrise and fulfill his obligation. However, he may not say the blessing of "Hashkivenu" after dawn (see Tosfos DH u'Vilvad).
2) THE FIRST TWO CHAPTERS OF TEHILIM ARE ONE
QUESTION: The Gemara says that the first two chapters of Tehilim were originally a single chapter. Why were they later divided into two chapters?
ANSWER: The MAHARSHA explains that, as the Gemara says, the eighteen blessings of the Shemoneh Esreh originally corresponded to the first eighteen chapters of Tehilim. When an additional blessing was added later to the Shemoneh Esreh (the blessing against slanderers; see the Gemara later, 28b), the first chapter of Tehilim was divided into two, so that the nineteen blessings of the Shemoneh Esreh would still correspond to the first nineteen chapters of Tehilim.