I would like to preface this by first saying I don't know shit. Judaism, and its princepts are a bit alien to me, and this is literally my first in depth experience with it. The following explanation is from a Rabbi, and his name along with the copyright is at the bottom, and I present it rather then offer up my own explanation because I believe you would rather have answers than my own possibly incomplete understanding

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Now, for the Jews I was studying with, they didn't believe in Satan. They believed the Serpent was sent by God in order to trouble man, and therefore had nothing to repent of. Personally, I believe the Serpernt was indwelt by Lucifer, and therefore beyond redemption, tying in with the seven thunders of Revelation.
Teshuva - Return
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"Let the wicked one leave his way and the sinful man his thoughts; let him return to HaShem and He will show him mercy; [return] to our God for He is abundantly forgiving." Yeshaya (Isaiah) 55:7
The word teshuva means return. If a person violates one of HaShem's commandments (mitzvos), he is required to "return" to God. Teshuva consists of three basic steps:
Admitting your sin(s) to HaShem. This step is called vidui. This is a private matter. In general it is not proper to tell other people about the wrong things you have done.
Feeling regret that you sinned.
Making a commitment not to repeat the sin.
A person who properly fulfills the mitzva of teshuva is forgiven for his sins.
Although the mitzvah of teshuva applies all year, it takes on special significance in the period preceding the holidays of Rosh HaShana and Yom Kippur. On these holidays we are judged for the past year and HaShem decides how we will be rewarded or, God forbid, punished. For this reason the month preceding Rosh HaShana, Elul, is a special time for teshuva.
It is very important to remember that everything we do for Rosh HaShana and Yom Kippur, such as praying, blowing the shofar, fasting, and all of the other mitzvos and customs of this time, will only earn us forgiveness for our sins if they are accompanied by teshuva. Empty acts will not accomplish this goal.
© Eliezer C. Abrahamson