1) AGADAH: "V'NAKEH" -- THE THIRTEENTH ATTRIBUTE OF MERCY
Rebbi Elazar points out a contradiction in the verse which lists the Thirteen Attributes of Mercy (Shemos 34:7). The verse describes Hash-m as "v'Nakeh" -- "Who cleanses [a person of his sins]," which implies that Hash-m grants atonement. However, the very next words say, "Lo Yenakeh" -- "He does not cleanse," which means that He does not grant atonement. Rebbi Elazar explains that atonement depends on whether or not a person does Teshuvah. Hash-m cleanses a person of his sins only when he repents.
Based on this Gemara, the BNEI YISASCHAR demonstrates a principle taught by REBBI DOV BER (the "Magid") of MEZRITCH, a close disciple of the Ba'al Shem Tov.
Rebbi Dov Ber of Mezritch proposes that the Thirteen Attributes of Mercy ("13 Midos Rachamim," as enumerated in Rosh Hashanah 17b) correspond to the thirteen exegetical methods with which laws are derived from the Torah ("13 Midos sheha'Torah Nidreshes ba'Hen," as listed in the beginning of Toras Kohanim, and as printed in the Sidur before the Shacharis service). (Rebbi Dov Ber's proposition is quoted by MAGID DEVARAV L'YAKOV #147, ARVEI NACHAL, Parshas Vayetzei, and by others, and is discussed at length by REBBI LEVI YITZCHAK of BERDITCHEV (Kedushas Levi, Parshas Ki Sisa).)
Rebbi Dov Ber of Mezritch explains that the first of the Midos with which laws are derived from the Torah is the Midah of "Kal v'Chomer." This corresponds to the first Midah of the Thirteen Attributes of Mercy, the word "Kel" (Hash-m's name). ("Kel" is the first of the Thirteen Attributes according to the Arizal; see Chart to Rosh Hashanah 17b. In addition, according to Kabalah, the Thirteen Attributes of Mercy are alluded to in the verses of "Mi Kel Kamocha" (Michah 7:18-20), as discussed by the TOMER DEVORAH. The first Midah mentioned in those verses is "Kel.") The Torah alludes to this correlation in the prayer of Moshe Rabeinu on behalf of his sister, Miriam, when she was smitten with Tzara'as. In order to arouse Hash-m's mercy for her, Moshe prayed for her with the name, "Kel" -- "Kel Na Refa Na Lah" (Bamidbar 12:13). Hash-m replied with a Kal v'Chomer ("Im Aviha Yarok Yarak...," see Bereishis Rabah 92:7 and Rashi to Bamidbar 12:14) to teach Moshe that in order to arouse the Midah of "Kel," one should apply the Midah of Kal v'Chomer. Similarly, Rebbi Levi Yitzchak adds that the Chachamim derive through a Kal v'Chomer that the dead will eventually be revived ("if those who never existed come to life, then certainly those who already have lived will come to life"; Sanhedrin 91a). When Miriam was afflicted with Tzara'as, Aharon said to Moshe, "Do not let her be like a dead person..." (Bamidbar 12:12). (Kedushas Levi, Parshas Ki Sisa)
The second of the Thirteen Midos is "Gezeirah Shavah," which corresponds to "Rachum" (according to the Arizal's count of the Midos Rachamim). A person who seeks to arouse his mercy, Rachamim, for a pauper should try to envision himself as a pauper; he should equate himself to the poor person, or make a "Gezeirah Shavah" between himself and the poor person. (Kedushas Levi ibid.)
The last of the Thirteen Attributes of Mercy is "v'Nakeh," the subject of the Gemara here. This Midah corresponds to the last of the Thirteen Midos sheha'Torah Nidreshes ba'Hen, which is the principle of "Shenei Kesuvim ha'Mach'chishim Zeh Es Zeh..." -- "when two verses contradict one another, a third verse compromises between them and resolves the contradiction." The Bnei Yisaschar (Chodesh Elul 2:8) cites his Mechutan, Rebbi Tzvi Hirsh of Ziditchev, who explains that this correlation is evident from the Gemara here. The two statements of "v'Nakeh" and "Lo Yenakeh" seem to contradict each other. The Gemara resolves the contradiction from a third verse, "v'Shavta Ad Hash-m Elokecha" (Devarim 30:2), which teaches the concept of Teshuvah. Thus, the thirteenth Midah sheha'Torah Nidreshes Bah reveals the meaning of the thirteenth Midah of Rachamim. (See also Ma'amarei Rosh Chodesh 4:3, Elul 2:7, Magid Ta'alumah to Berachos 34a, and many other places in the works of the Bnei Yisaschar.)
RAV DAVID COHEN, shlit'a, in MAS'AS KAPAI (on Tefilah) adds that perhaps this is one reason why the Thirteen Midos sheha'Torah Nidreshes ba'Hen are recited before Pesukei d'Zimra every morning. They are recited in order to arouse Hash-m's Thirteen Attributes of Mercy to which they correspond.
2) CONFESSING SINS FROM ONE'S PAST
QUESTION: The Gemara cites an argument with regard to whether or not one should confess his old sins each year, even though he confessed them in previous years. According to the Tana Kama, to confess one's old sins is abhorrent, while Rebbi Eliezer ben Yakov maintains that it is praiseworthy.
Why does the Tana Kama say that it is abhorrent to confess one's old sins? What is the proper way to conduct oneself in practice?
ANSWER: RABEINU YONAH (end of SHA'AREI TESHUVAH) explains that there are three different ways in which one might confess his sins of previous years.
(a) One who confesses only his sins of previous years and omits mention of sins of the outgoing year certainly acts improperly. It is as if he says that he considers himself to be righteous and free of sin except for those sins which he committed in previous years. His confession lacks the element of humility needed for Teshuvah and displays a sense of arrogance.
(b) Similarly, one should not even mention his old sins together with his new sins, according to the Tana Kama, because doing so shows that he does not have confidence that Hash-m pardons those who do Teshuvah.
(c) However, requesting atonement in general is different from confessing specific sins. Part of the Mitzvah of Viduy is the sinner's iteration of each sin. This confession must be done every year for sins committed that year. On the other hand, since the penitent sinner performed the Mitzvah of Viduy last year, he should not mention any specific sins from that earlier year. Nevertheless, he should continue to request a general forgiveness for past misdeeds, just in case he did not fully repent for those sins. An additional benefit of requesting a general forgiveness for past sins is that if further afflictions have been decreed upon him because of the old sins, perhaps extra confession now will lessen the severity of his suffering. Furthermore, a request for forgiveness now will help for sins which he remembered only after last year's confession.