In Ha’azinu, the penultimate parashah of the Torah, Moshe delivers his message in song. Although the parashah is replete with poetic allusions, the starting point for Moshe’s address is his call upon heaven to bear witness.
Give ear, oh heavens and I will speak, and hear, oh earth, the words of my mouth. (D’varim 32:1)
This is not simply a case of poetic license; Moshe’s opening statement is a crucial part of his message. In fact, in the verses that lead up to this poetic speech, Moshe gives notice of his intention to call upon heaven and earth as witnesses:
Gather to me all the elders of your tribes, and your officers, that I may speak these words in their ears, and call heaven and earth to witness against them. (D’varim 31:28)
This testimony was mentioned earlier, as well:
I call heaven and earth to witness on this day against you, that I have set before you life and death, blessing and curse; therefore choose life, that both you and your descendants may live. (D’varim 30:19)
What is the purpose of calling heaven as a witness? The simple answer is that Moshe will soon be leaving the stage; he knows that his death is imminent, and that he will no longer be there to chastise the people should they go astray. Therefore, he informs them that there are other, more permanent witnesses who will always be there to testify in his stead.
Similarly, in his treatise on the Laws of Teshuva (repentance), Rambam refers to a different sort of “supernatural testimony:”
What constitutes teshuvah? That a sinner should abandon his sins and remove them from his thoughts, resolving in his heart never to commit them again.... Similarly, he must regret the past, as [Jeremiah 31:18] states: "After I returned, I regretted." He who knows all mysteries will testify that he will never return to this sin again … He must verbally confess and state these matters which he resolved in his heart. (Rambam Teshuva 2:2)
Rambam states that one of the critical elements of teshuva is that “He who knows all mysteries,” God Himself who alone knows the future behavior of each and every one of us, testifies that this particular person will never repeat this sin. This passage has been much debated, with some opining that it indicates Rambam’s belief that the recidivist sinner’s behavior voids his penitence. The sin of which he was originally guilty still stands, unforgiven and uncleansed, because his later repetition of the sin proves that his penitence was insincere. In this view, a sinner is forgiven only if he or she never backslides or regresses into old, die-hard behaviors. Only when God Himself is able to attest that the sin was never revisited is the sin expunged from the sinner’s record.
Rav Yisrael Salanter took issue with this interpretation, noting that if this were the case, the stages of repentance in Rambam’s formulation would have appeared in a different sequence: The reference to Divine testimony should have followed the words “resolving in his heart, never to commit (that sin) again.” Instead, the testimony of “He who knows all mysteries” regards the penitent’s regret. Therefore, Rav Yisrael Salanter theorized, Rambam’s statement regarding God’s testimony is not telling us as much about the penitent’s future behavior as it is about his or her current sincerity: A person must express regret for their sin with such sincerity that they are willing to call upon God as their witness. God’s testimony regards the penitent’s sincerity in the present tense, and does not attest to events that may or may not transpire in the future. Therefore, if a person is sincere in their teshuva, they are forgiven - even if they stumble and fall again in the future.
This reading of Rambam’s comments reveals a far more realistic view of human nature: There are - and always have been - times when even sincere penitents succumb to the Evil Inclination. The Talmud teaches that part of the insidiousness of sin is that it becomes habitual.
… R. Huna said: ‘Once a person has committed a sin once and twice, it is permitted to him.’ Permitted?! How could that occur to you? Rather, it appears to him as if it were permitted. (Talmud Bavli Yoma 86b)
While it may be the case that before a first offence a person undergoes an internal struggle, at a certain point the battle is won or lost and the struggle is over; the desire for immediate gratification overcomes the voice of long-term, logical thinking. The habitual sinner, on the other hand, no longer struggles; he creates a “new normal.” However, if this person gathers the strength to do sincere teshuva, and, despite the sincerity of his or her remorse and resolve never to sin again nonetheless falls prey to the Evil Inclination, he or she will experience a new struggle – perhaps even more fierce than the first. This sin is not a case of “business as usual;” the habit of sin has not been allowed to dictate behavior. The burning desire he or she once had for that particular sin had already been extinguished through sincere teshuva. The more recent sin is the result of a new struggle, a new “fire,” unrelated to the previous episode for which he or she had already been forgiven.
Rabbi Soloveitchik focused on the significance of God’s involvement in this process: By virtue of being descendants of the matriarchs and patriarchs, each and every Jew is endowed with a special holiness. This holiness was given full expression in the covenant of Mount Sinai. It is this covenant that insures that an individual’s status as a Jew, and the status of the Jewish People as God’s chosen nation, can never be forfeited.
However, in the book of D’varim another covenant was forged between God and each Jew as an individual. When a person transgresses, it is this covenant that is broken. Behavior that violates this covenant will result in the forfeit of the privileges that this covenant with God endows.
Sin has a way of corrupting us; beyond the bad behavior, it sullies the sinner’s soul. Teshuva seeks to correct sin on two distinct levels, first by achieving forgiveness for the behavior itself, but also by cleansing the soul, freeing it from the burden with which sin has saddled it. Sin creates a distance between the two parties to the covenant; even when the misdeed itself is forgiven, the estrangement remains. Trust must be rebuilt; the sanctity of the covenant must be restored. By bringing God into the equation, by summoning God as a witness of one’s repentance, we replicate the forging of the covenant, in a manner akin to renewing vows. Just as heaven was called as a witness by Moshe, so, too, must the penitent invoke Heaven as a witness when he or she renews the covenant. The process of teshuva described by Rambam, in which God testifies to the sincerity of the teshuva, creates a parallel with the testimony of heaven and earth Moshe invokes before his death. Both are intended to enable us to connect – or reconnect – with the holiness our souls sorely need.
The Mishnah in which the Yom Kippur ritual is described in detail, Tractate Yoma, concludes with an optimistic teaching by Rabbi Akiva:
Rabbi Akiva said: Fortunate are you, Israel! Who is it before whom you are purified? And who is it that purifies you? Your Father in Heaven, as it is said: ‘And I will sprinkle pure water upon you and you shall be pure.’ And it further says: ‘The hope (mikveh) of Israel is the Almighty!’ Just as the mikveh purifies the impure, so does the Holy One, blessed be He, purify Israel. (Mishna Yoma 8:9, Talmud Bavli 86b)
In this uplifting summary of the process of teshuva, Rabbi Akiva leads us away from the cold, impersonal accounting of sin and punishment, atonement and purity that is the world of jurisprudence; indeed, a judge would be likely to “throw the book” at the recidivist sinner. Instead, Rabbi Akiva draws a metaphor from the world of ritual purity. Surely, this metaphor supports a more forgiving understanding of teshuva: A person who immerses in the purifying waters of the mikveh will most certainly – inevitably, unavoidably – become impure again. And yet, this in no way impacts or diminishes the purity that is achieved in the present moment. So, too, a person who sins and repents – sincerely and wholeheartedly enough to invoke God as their witness – is forgiven, even if they repeat their sin in the future.
Regret is a powerful tool; it allows us to erase the past. Standing before God and expressing regret not only liberates us from the past, it allows us to renew our personal covenant with God. Sincere teshuva creates a moment of purity, in which God purifies us as if with pure waters of the mikveh, leaving us cleansed and holy. Even if we subsequently stumble, and are in need of cleansing once again, that moment of purity is not sullied by the specter of whatever missteps lurk in the future.
For a more in-depth analysis see: http://arikahn.blogspot.co.il/2016/10/parashat-haazinu-and-yom-kippur-audio.html
 See R’ Yitzchak ben Nisim Rietbard, Beit Yitzchak, Drasha for Yom Kippurim.
 Rav Yisrael Salanter, Kochvei Ohr; also see Rabbi Menachem Krakowsky, Avodat Hamelech Laws of Teshuva 2:2.
 This position is taken by Rav Sa’adya Gaon, Ha’emunot v’Hadeyot maamar 5. It may also be the intention of the Sefer HaChinuch Mitzva 311.
 R. Yaakov Lorberbaum (1770-1832), Nahalat Yaakov; Rambam, Laws of Teshuva 2:2.
 Rabbi Yosef Dov Soloveitchik, Reshimot Shiurim, Nedarim 8b.