Rebbe Nachman explains (Likutei Mohoran I, 8) that this process of teshuvah for our sins starts with feeling regret and sighing over what we’ve done. When we take a new breath with a yearning to change and we express our remorse in a sigh to Hashem, we break ourselves free from our past mistakes and breathe new life into our souls. Of course, if we’re also able to express our feelings in words, this is an even higher level of teshuvah.
However, at the end of the day, the ultimate tikkun for our sins comes through fixing our seichel. The Zohar HaKadosh says that the source of all the birurim (clarifications of good and evil) comes from our thoughts. In other words, the way that we see the world, other people, and ourselves has a tremendous effect in all the spiritual and material realms. For example, if we think that a piece of fruit is just a product of the laws of nature which caused a tree to collect water, sprout a bud, and eventually form a fruit, then we give power to the exterior “shell” – physical reality – of that fruit to hide the goodness of the sparks of kedushah that are contained within it. On the other hand, when we say a brachah with kavanah and we remind ourselves that this piece of fruit was created solely by the Master of the Universe, we “peel off” the “shell” of the darkness of the material world, so to speak, and we reveal the amazing light of goodness that is concealed inside the fruit.
The same thing is true about every other aspect of creation. When we focus on the inner spiritual reality of something, our thoughts clarify and separate out the good from the bad. Our minds elevate the kedushah back to its source and discard the material shell of contamination.
As we mentioned above, this is essentially the entire purpose of the Torah, which teaches us the difference between good and evil. By studying and following the laws of the Torah, we clarify every aspect of the universe – what is permitted and what is prohibited, what is pure and what is contaminated, and so on.