Aveira:

Separates one from G-d:[1] Every sin is likened to idolatry and separates one’s soul from G-d for that moment. When one sins, he is more distanced from Hashem then even the Kelipos and Sitra Achra. He is more distanced than idolatry, impure animals and creatures.

Rabbinical sins:[2] Although Rabbinical commands and decrees were not directly commanded by Hashem and the Torah, transgressing them is very severe, and has spiritual effect just like a Biblical transgression. The Alter Rebbe states in Tanya that one who transgresses even a light Rabbinical prohibition is separated from G-d for that very moment of the sin, just like by actual idolatry.

Ruach Shtus:[3] The Sages[4] state that a person does not transgress a sin unless a spirit of folly enters him. This means that the person sins due to being cloudy minded and not thinking through the reality of the results of his sin. He thinks he can remain attached to Hashem despite the sin, when in truth every sin is likened to idolatry and separates one’s soul from G-d for that moment. This is similar to a married woman who gets seduced into sinning with another man. At the time of the sin she is lightheaded, not taking into account the betrayal and ultimate damage this will do to her relationship with her husband, her family and in essence herself. The lust she has clouds the reality of the situation and challenges her to make a grave mistake that defies intellect. The same applies by all sin, that the Kelipa garbs one’s G-dly soul and prevents its expression of reason to prevent the sin.

Every sin has different purgatory:[5] Every sin a person does blemishes a part of his connection with G-d. To repair this tear one must go through suffering either in this world or the next. Every sin makes a unique tear that requires a unique form of cleansing and punishment that is specified for that sin. This applies even for those categories of sins that carry a penalty of excision or death by Beis Din, nevertheless, each blemish and consequent punishment is truly unique. The purpose of this punishment is to cleanse and remove the dirt and blemish that was created due to the sin.

One who sees an Aveira transpire:[6] Man should be aware that whatever he witnesses contains a Divine intent. One who sees a sin transpire by another, has not been shown this sin for naught. Hashem showed him the sin as Divine providence to hint to him that he too is guilty of the sin on some level. Even if one knows that he never actually committed such a sin, perhaps he has contemplated this sin, and it is known that the thought of a sin is [in certain aspects] even more severe than the actual sin itself.

The imprint of an Aveira gets on Hashem when one attaches to Him:[7] When one sins and then Davens to Hashem, attaching to Him through prayer, the imprint of the Aveira Kevayachol gets onto Hashem. This is similar to a dirty stamp which is placed onto wax, in which case the dirt also cleaves to the wax. This sin causes dirt and blemish above. This is an additional motivation to abstain from sin, in order not to damage one’s connection with Hashem.

The proper reaction when witnessing another perform a transgression:[8] When one sees another Jew performing a transgression, or hears of such a transgression having been performed, one’s immediate reaction should be to try to find that sin within his soul. It may not be the exact sin in quantity and quality as that which was witnessed or heard of, however one is to search for a similar matter in his soul that corresponds in some way to that sin. The purpose of Hashem giving him the knowledge of this sin is to reveal to him that he can fix this aspect of his soul. When one goes ahead and repents for his corresponding sin it can then cause the original sinner to also repent. This can be accomplished through one intending to unite with the Rasha, and when he does so and repents, he helps initiate a movement of Teshuva within the person.

The 17 contemplations to hinder one from sin:

The Sefer Chareidim records 17 conditions for Mitzvah fulfillment. The following are the 17 contemplations that one should entertain prior to committing a sin:

1. Contemplate until where the blemish of one’s sin can reach.
   1. Contemplate against whom one is rebelling.
   2. Contemplate who is watching him sin even in private.
   3. Contemplate that instead of using one’s time for serving G-d one is using it to rebel against him.

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[1] Tanya chapter 24

[2] Tanya Chapter 25

[3] Tanya chapter 24

[4] Sotah 3a

[5] Tanya chapter 24 in gloss

[6] Or Torah [Maggid] Vayikra 107

[7] Or Torah [Maggid] Vayikra 107

[8] Keser Shem Tov 89; Toldos Yaakov Yosef Lech Lecha 17a