Gemara

Mishnah: We do not stop in the middle of the Klalos.

Question: What is the reason?

Answer #1 (R. Chiya bar Gamda): "My son, do not despise the rebuke of Hash-m."

Answer #2 (Reish Lakish): We do not bless on punishments.

Beraisa: The one who reads the Klalos starts a verse before them, and reads a verse after them.

Abaye: This applies to the Klalos in Vayikra, but not to those in Devarim.

Question: What is the reason?

Answer: The Klalos in Vayikra were said in the plural ("Im Lo Tishme'u..."), and Hash-m said them through Moshe. Those in Devarim were said in the singular, and Moshe said them (with Ru'ach ha'Kodesh).

Levi bar Buti said the Klalos in Devarim b'Gimgum (he hurriedly muttered them, for he was distressed to say them). Rav Huna told him that one may stop in the middle of the Klalos in Devarim.

Beraisa - R. Shimon ben Elazar: Ezra enacted that we should read the Klalos in Vayikra before Shavu'os, and those in Devarim before Rosh Hashanah.

Abaye: This is so the Klalos should be completed when the year is finished.

Question: This does not explain those in Vayikra!

Answer: It does!

Mishnah: The world is judged on Shavu'os regarding fruits (it is also like a Rosh Hashanah).

Rishonim

The Rif and Rosh (4:10) bring our entire Gemara.

Ran (DH Gemara): One must bless on the bad like he blesses on the good. This refers to accepting Hash-m's decree. When one comes to read the Torah, he should arrange not to bless on Klalos.

Ran (ibid.): Really, the Oleh must read more than one verse before and after, since we do not read less than three verses from a Parashah.

Ran (ibid.): Even though Hash-m agreed to Moshe's curses, still they are not as severe, and one may (stop in the middle, for one may) bless on them.

Question: When there are two Shabbosos (that are not Yom Tov) between Rosh Hashanah and Sukos, we read Netzavim (before Rosh Hashanah) and va'Yelech (after Rosh Hashanah) separately, even though altogether they are only 70 verses. We should rather read Matos and Mas'ei separately (together they are over 240 verses), and Netzavim and va'Yelech in one week (and still the curses in Ki Savo would be finished before Rosh Hashanah)!

Answer #1 (Ran ibid.): Nowadays we read the Klalos before the Shabbos before Rosh Hashanah and Shavu'os.

Answer #2 (R. Nisim, brought in Rosh ibid.): The curses end in the beginning of Parashas Nitzavim.

Rambam (Hilchos Tefilah 13:7): We do not interrupt the Klalos in Vayikra. Rather, one person reads all of them. He starts a verse before them, and ends one verse after them. One may interrupt the Klalos in Devarim, but the custom is not to.

Kesef Mishneh: The Yerushalmi says that we say the Klalos in Vayikra b'Gimgum, but we may read those in Devarim normally.

Tosfos (DH Ein, citing Yerushalmi1 26b): R. Acha says that one person reads all of them due to "Musar Hash-m Beni Al Tim'as v'Al Takotz b'Sochachto" - do not make His rebuke Kutzim (chopped up). R. Yehoshua of Sichnin learns from "Imo Anochi v'Tzarah" - it is not appropriate for My children to bless Me for their afflictions. Rather, one starts reading before the Klalos and finishes after them, so he can bless before and after on other matters.

Question: At the time of the Mishnah, the first Oleh blessed beforehand and the last Oleh blessed afterwards, and the others did not bless!

Answer (Taz 5): It was permitted to rely on the Berachos of the first and last, but one could opt to bless himself. This is like Berachos for food; everyone may bless by himself, or one may bless for everyone. It is unreasonable that if one did not hear the Berachah beforehand, e.g. he entered late, that he would read without a Berachah. Nowadays everyone blesses by himself, so one person must read all the Klalos.

Poskim

Shulchan Aruch (OC 428:6): We do not interrupt the Klalos in Vayikra. Rather, one person reads all of them. He starts a verse before them, and ends one verse after them. One may interrupt the Klalos in Devarim, but the custom is not to.

Magen Avraham (8): Nowadays the custom is that in Vayikra we begin with the Klalos themselves, because the Av Beis Din reads Shelishi, and this extends until the Klalos. It is better that the Rav pardon his honor and read fourth this week, or that the one who reads the Klalos should preface them by repeating the three verses before them. Keneses ha'Gedolah says that their custom is for the Rav to read the Klalos. Beforehand he says "Musar Hash-m Beni Al Tim'as...; Ki Es Asher Ye'ehav Hash-m Yochi'ach". We read them in a low voice (but loud enough for everyone to hear).

Kaf ha'Chayim (35): The Rav reads the Klalos, because it is most appropriate that he rebuke people.

Kaf ha'Chayim (32): Likewise, we do not interrupt the 'Arurim' in Ki Savo.

Kaf ha'Chayim (34): Sefer Chasidim is particular not to call a great person for the Klalos, lest his words be fulfilled. The Maharil is not concerned if the Shamesh hired for this is called. The Keneses ha'Gedolah says that there is no concern at all, for the reader does not intend to curse.

Mishnah Berurah (17): If one is called to read the Klalos he must do so; one who declines to read the Torah shortens his life (Berachos 55a). Nothing bad will happen because he reads. Since it is for Kavod ha'Torah, "Shomer Mitzvah Lo Yeda Davar Ra". In many places the Ba'al Korei himself reads. This is good. If he is a Kohen, in Bechukosai he can read from the beginning of the Parashah. In Ki Savo seven can read before him, and he will finish the Parashah.

Rema: Our custom is not to call someone by name to read the Klalos. We call one who wants to read them.

Bi'ur Halachah (DH bi'Shmo): This means, we call someone whom we already know that he will agree to read them. It seems that the Machatzis ha'Shekel explains that we announce 'Anyone who wants to read, come and read'; this is wrong.

Mishnah Berurah (19): We do not call someone lest he refuse, and transgress "v'Al Takotz b'Sochachto".