Should I Punish Myself for a Sin That I Did?
The true basic meaning of repentance is abandoning sin, and this is one of the universal commandments in the Torah.
How is this accomplished?
In the preamble to “Laws of Repentance” in Mishneh Torah, the book of Torah Laws compiled by Maimonides (“Rambam”), he writes that repentance entails one positive command: that the sinner turn away from committing his sin before G‑d, and confess to G-d.
This is the basic meaning of the Hebrew word teshuvah (“repentance”, or “return” to G-d) – to return to obeying G‑d with all one’s heart and soul, to serve Him, and to observe all of one’s commandments. (For Gentiles, these are the details of the 7 Noahide Commandments and their offshoots.) This is stated in Isaiah 55:7 – “Let the wicked person abandon his [wicked] path, and the sinful person [abandon] his [sinful] thoughts, and return to G‑d …” Likewise it is stated in Deut. 30:2, “You shall return unto the L-rd your G‑d and hearken to His voice [i.e. His words that He directed to us through His true prophets] … with all your heart….”
Repentance in general is the process of returning to be resolved to follow G‑d’s will, which is that the person should live in this physical world and observe what G-d has commanded for him, and to refrain from committing sins. This can be applied to any particular sin that a person may commit. This differs from the common misconception that repentance is synonymous with afflicting one’s self (for example, by fasting or other means) on account of one’s sins.
Even in the case of deliberate sins so severe that one is liable to death as a punishment from G-d – for which one’s atonement may need to be made complete by suffering after he repents – this means that it is G‑d Who brings the required suffering upon the forgiven sinner, in the required manner and amount, in order to complete his atonement.
This is clearly specified in Psalms 89:23 which teaches, “With a rod shall I [G-d Himself] remember their sin, and with afflictions their iniquity.” In other words, when G‑d finds that the person’s repentance is acceptable, as the person returns to Him with his full heart and soul, then following this initiative undertaken by the person, this arouses G‑d’s love and kindness to scour away the person’s forgiven sin through affliction in this physical world.
This is a kindness extended by G-d to those who sincerely repent, so there will be no need to subject the person’s soul to any suffering in the afterlife, which is necessarily a much more severe and painful process. If a person passes away without having repented for his sin, the required correction might entail subjecting the soul for an extended time to the much worse pains of Gehinom (the realm of spiritual purgatory).
This is the meaning of the verse (Prov. 3:12), “For he whom the L‑rd loves, He [G-d Himself] chastises [in this world]…” Therefore, Maimonides and other codifier’s of Torah Law make no mention any types of self-punishment (not even fasting or self-mortification) in regard to the means of fulfilling the commandment of repentance, even in the case of capital sins.
From this we learn that self-punishment is not required even for sins that are so severe that the person’s atonement is completed through suffering. Therefore, if anyone says, “I need to punish (or harm) myself because of my past sin,” that is a false idea, which is to say that it goes against the teachings of G-d’s Torah. The essential point is that even the suffering that (along with repentance) brings about complete atonement for capital sins is not to be self-inflicted. Rather, it is imposed upon the person by G-d through Divine Providence. How much more does this lesson apply for any misdeeds the person commits, deliberately or accidentally, that are not as severe as capital sins.
 That being said, no human has the right or ability to judge as G-d judges, so we must not be unsympathetic to another person’s suffering by rationalizing that “he must deserve it.” G-d obligates us to cheerfully help others in need, heal the sick, give charity for the poor, etc., and He rewards us for doing so. Furthermore, we have faith and trust in G-d that seemingly negative occurrences come from Him, and since He is the ultimate good, those difficulties really contain hidden good.
 However, there is a means by which a person can actively bring atonement for himself, and that is by generously giving proper charity and doing acts of goodness and kindness for others.
 Exodus 23:5 states: “When you see the donkey ['chamor' in Hebrew] of your enemy lying under its burden, and you would be refraining from helping it, rather, you must help it.” The Baal Shem Tov taught that in Hebrew, the word “chamor” (donkey) is spelled the same as the word “chomer,” which means “materiality,” i.e., the physical in general, and in particular, the physical body. So he interpreted the verse as follows:
“When you see the ‘chomer,’ ” your physical body, as your enemy, and it is “lying under its burden” that has been placed upon it, you may think of “refraining from helping it” – to fulfill it’s mission from G-d – and instead you will follow the path of mortification of the flesh to break down the body’s materiality. However, not in this approach will the Divine light of Torah reside. Rather, “you must help it” – purify the body and refine it in health, but do not break it by mortification.
The underlying principle in this teaching is that the physical human body is G-d’s prized creation and possession, so much so that He sends a spiritual soul down from the Heavenly realm to enliven it to fulfill a mission for Him in this world. The reward G-d gives to one’s body and soul for enduring and carrying out their lifelong mission, within the context of observing one’s commandments, is resurrection in the World to Come, at which time G-d will heal the resurrected body of any and all wounds and defects it suffered, so it will be an immortal perfect body re-enlivened by that same soul, and the physical flesh of the resurrected body will experience G-dliness.
 The Talmud discusses the fact that G-d in His love and mercy brings atonement for lesser sins through lesser types of suffering – i.e. the minor discomforts, aggravations or inconveniences that befall a person in the “normal” course of his life by Divine Providence. For example, if a person accidentally stubs his toe, or reaches into his pocket for a dime and pulls out a penny instead, he should say a quick prayer to G-d that this momentary pain, inconvenience or aggravation – which came to him only by G-d’s individual Divine Providence – should please serve as an atonement for his sins. This realization is also key to helping a person overcome his natural tendency to get easily angered, aggravated, offended or stressed.
*This answer is based on Chapter 1 of “Igeret Ha’Teshuva” by Rabbi Shneur Zalman of Liadi.