This week's parsha Ki Sisa, and Parshas Parah (one of the four Parshios), have an internal connection. In Ki Sisa we learn of the Cheit HaEgel (the Sin of the Golden Calf), and how Moshe Rabbenu obtained forgiveness for the entire Jewish People, while Parshas Parah discusses the mitzva of the Red Heifer (Parah Adumah). The ashes of the Parah Adumah were used to cleanse a person who had become impure through contact with a meis (corpse).
Every physical mitzva we do has a spiritual service to Hashem. Parah Adumah represents the mitzva of teshuva. Physically, when someone becomes impure because he had contact with something lifeless, he needs to be cleansed from that impurity with the ashes of the Parah Adumah; similarly when someone disconnects himself from Hashem, he becomes Tomei Meis in a spiritual sense and he has to do teshuva to return and reconnect himself to Hashem – which is life – as the possuk says “and you who are attached to Hashem, your G-d, are alive today.” How is it possible for a person to detach himself from Hashem – a spiritual death – by doing something against Hashem (an aveira). The Yetzer Hora tells him that this action does not disconnect him from Hashem, but this is a lie.
At Matan Torah Bnei Yisroel became free of the Yetzer Hara. The Aseres Hadibrois were carved out of stone, as the Torah says, charos al haluchos, the Mishna says don't read charos – carved, read cheirus – freedom, as it is known that by Matan Torah the Jewish people became free of the Yetzer Hara and free of the Angel of Death. The filth created by the sin of the Aitz HaDaas returned when they sinned at the Cheit HaEgel, bringing back the Yetzer Hara and the Angel of Death. Here we see the connection between the Cheit HaEgel and spiritual and physical death. Rashi explains that the Parah Adumah came to forgive for the Cheit HaEgel. The Medrash says that the Parah Adumah is like the cow who has to wipe up the filth of the calf which is red, representing sin.
The Parah Adumah is the only korban (sacrifice) that is brought outside the Beis Hamikdosh to atone and cleanse for the sin of the Cheit HaEgel; but to be able to do that you must be connected to Hashem. That is why the blood has to be sprinkled towards the Bais HaMikdash and the Kohein had to be able to see the opening of the Haichal from outside (this is why the eastern wall of Har Habayis was lower, so there could be an uninterrupted view of the Heichal. With these ashes you cleanse someone who is physically Tomei Meis. The same way teshuva helps someone who became Tomei Meis spiritually. Teshuva helps even more than a sacrifice.
A korbon (sacrifice) in the Beis Hamikdosh only obtained forgiveness for accidental sins. Teshuva can work on sins which were done purposely or were done by those who rebelled. That is the power that Hashem tells us, let someone do teshuva and he will be forgiven. Even if you are outside because of your actions, if you focus your eyes and heart towards the Heichal because the Aibishter is there, you are getting the power to do teshuva. As the ashes had to be constantly available so that any time it was necessary it could be used, this teaches us that the power of teshuva must be by a Jew constantly, so he knows that he can always do teshuva. Even a tzadik has to know that he has to have the power of teshuva, since it is stated that if someone lives in a generation during which the Bais Hamikdosh was not rebuilt, it is if it was destroyed in his generation. If there would be one tzadik who would be able to tip the world to the good the Beis HaMikdash would be rebuilt. So when the Tzadik realizes this it arouses within him a deeper feeling of teshuva and reunification with Hashem, and especially those who are not tzadikim. The lesson of this week's parsha is for all of us. Before we can learn about the Korban Pesach and which represents freedom and geula, there has to be the cleansing of the Parah Adumah (teshuva). That is the reason why we have to read the Parsha of Parah Aduma before Parshas HaChodesh which represents the month of Nissan – the month of Geula.
Likutei Sichos, Vol. 16