1) ONE SIN WHICH IS CONSIDERED LIKE TWO
OPINIONS: Rav Nachman asked Rebbi Yitzchak what the verse means when it says, "My nation committed two evils" (Yirmeyahu 2:13). Rebbi Yitzchak answered that the verse means that the nation committed one evil which is equal to two. This refers to the sin of Avodah Zarah.
In what way is the sin of Avodah Zarah considered like two sins?
(a) RASHI says that Rebbi Yitzchak's teaching relies on the verse cited by the Gemara shortly afterwards. The verse (Yirmeyahu 2:10) states that the people of the islands of the Kitiyim and the people of the land of Kedar never deserted their gods even though they were worthless. "One transgression which is equal to two" means that the Avodah Zarah of the Jews at that time was worse than the two idols of the Kitiyim and the Kedarim combined. When those nations went into exile, they brought their idols with them and remained loyal to them. In contrast, when the Jewish people went into exile, they deserted Hash-m and they began to serve Avodah Zarah.
(b) RABEINU GERSHOM also explains that Rebbi Yitzchak's teaching refers to the verse cited later. He explains that the two evils contained within one transgression were that the Jews served the idol of the Kitiyim and the idol of the Kedarim.
(c) The ETZ YOSEF and AHAVAS EISAN (in the EIN YAKOV) explain that the sin of Avodah Zarah was equal to two sins because one who commits idolatry transgresses both the Mitzvas Aseh of "Anochi Hash-m Elokecha" and the Lo Ta'aseh of "Lo Yiheyeh Lachem Elohim Acherim." In that sense, Avodah Zarah is one sin which includes two.
Moreover, the first commandment of the Aseres ha'Dibros, "Anochi Hash-m Elokecha," is the root of all Mitzvos Aseh, and the second commandment, "Lo Yiheyeh Lachem Elohim Acherim," is the root of all Mitzvos Lo Ta'aseh. The sin of Avodah Zarah is equal to the two Mitzvos which are the root of the entire Torah.
(d) The MAGID of DUBNO explains as follows. When other nations served Avodah Zarah and exchanged their god for another one, it was not so terrible. They merely exchanged nothing for nothing. Since they were justifiably disappointed with their first god and his failure to respond to their prayers, they changed their allegiance to a new god. In contrast, it was a terrible transgression for the Jewish people -- who saw the great power of Hash-m and were the beneficiaries of His great kindness -- to give up Hash-m in order to serve useless and powerless idols. Accordingly, there were two evils in their sin of Avodah Zarah: they left the Almighty Hash-m, and they changed their allegiance to entirely worthless idols in His place.
2) YAKOV AVINU DID NOT DIE
QUESTION: Rebbi Yitzchak says that Yakov Avinu did not die. Rav Nachman asks how could Yakov Avinu not have died -- the Torah says that the people eulogized him, embalmed him, and buried him (Bereishis 50:1-15). Rebbi Yitzchak answers with an inference from the verse which compares Yakov to his children. Just as his children are alive, so, too, he must be alive.
How does Rebbi Yitzchak's response address the fact that the Torah describes Yakov Avinu's burial?
(a) The CHOCHMAS MANO'ACH explains that Rebbi Yitzchak does not mean that Yakov is still alive today. Rather, it means that he was still alive when he was returned to Eretz Yisrael for burial in the Me'aras ha'Machpelah. The people mistakenly thought that he was dead and thus they eulogized him and embalmed him (just with fragrances, as Rashi points out in Bereishis 50:2).
The reason he remained alive until his return to Eretz Yisrael is because Hash-m promised that He would bring him back to Eretz Yisrael. In fulfillment of His promise, Hash-m ensured that Yakov Avinu was brought back to Eretz Yisrael before his Neshamah left his body. Similarly, the Gemara in Sotah (13b) explains how Rivkah's prophecy, "Why should I be bereaved of both of you in one day?" (Bereishis 27:45), was fulfilled. Just before Yakov Avinu was buried, Chushim ben Dan killed Esav and his head rolled onto Yakov's lap and Yakov smiled.
(b) The KLI YAKAR (Bereishis 47:29) explains Rebbi Yitzchak's statement based on the principle that "Tzadikim are called alive even in their deaths, and Resha'im are called dead even when they are alive" (see Berachos 18a-b). When the Gemara here says that Yakov "did not die," it means that even though he died he was considered still alive because he was a Tzadik. The Gemara specifically mentions Yakov, and not Avraham or Yitzchak, because he was a Tzadik and all of his children were Tzadikim (in contrast to Avraham and Yitzchak, who each had a son who was not a Tzadik). Since children are considered a continuation of their father as long as they are alive, their father is considered alive as well. If, however, one's child is a Rasha, his father is not considered alive because "Resha'im are called dead even when they are alive."
This is also the intention of Rashi (in Bereishis 18:19) when he says that one who dies and leaves behind a child who is a Tzadik is considered alive. Indeed, Rebbi Yitzchak derives his teaching from an inference in the verse which compares Yakov to his children. Yakov Avinu is considered alive because he lives on through his children, who are Tzadikim.