It is part of our tradition that we may atone for sins all the time. Whether they are sins against human beings or against God. Teshuva, repentance, is open to us constantly. So why do we need one special day of the year, Yom Kipur?
One answer is that Yom Kipur is for the really serious sins, whereas the rest of the year you can atone for more mundane things. Although there’s another point of view that some terrible crimes are never forgiven ion this earth.
The Torah this week lays out the difference in an ambiguous way that allows for two options
“For on this day He will atone for/on you to purify you from all your sins before God you will be cleansed” (Chapter 16 verse 30).
Depending on where you put the comma, this can be understood to mean that this day atones for all your sins and you can be cleansed. The comma goes after “sins.” So, it might include all those sins you forgot to atone for or maybe did not even realize you may have done. Yom Kipur therefore takes care of everything.
Yet tradition has it that if I have offended someone, I can only make up for it directly with the person I have wronged or offended. We have no notion in Judaism of someone forgiving on behalf of someone else, or indirect atonement. It must be done directly.
The second version puts the comma in after God. In which case, it is saying that Yom Kipur only atones for sins before God. Not against other humans. And that is something you can do anytime throughout the year. Indeed, we now have a tradition that every Rosh Hodesh is a mini day of Atonement. Yet ever here opinions are divided as to whether it works only for God, or only man.