The Baal Shem Tov zt’l said he achieved his levels through immersing himself in the mikvah.
We don't have the parah adumah to attain taharah, but we still have the mikvah, which also purifies us immensely.
The Rishonim teach us that mikvah also removes the tumah of aveiros. The Shlah Hakadosh (Shaar HaOsiyos 9, Taharah) writes, "Fortunate is the one who always accustoms himself to have purity. It cleans away all tumos, including the tumah of aveiros."
Or Zarua writes, “Aveiros cause tumah. The Midrash on (Tehillim 51:4) מעוני כבסני הרב טהרני ומחטאתי, 'Cleanse me a lot from my sin, purify me from my iniquity' teaches that whoever commits an aveirah, it is as if he became tamei from a dead person. I learned from Rabbeinu Simchah, ‘All people who want to do teshuvah must go to the mikvah.'
A story is told in Avos d’Rabi Nosson (3) about a girl captured by gentiles. When she was freed, they brought her to a mikvah because she had eaten the food of non-Jews. Non-kosher food doesn’t make a person tamei. Nevertheless, they had her tovel to cleanse her from the aveirah..."
That mikvah purifies us from sins shouldn't surprise us because one of the primary reasons everybody goes to the mikvah on erev Yom Kippur is to purify themselves from aveiros.
The Radvaz (vol.3 415) states, "To do teshuvah for every type of sin, one needs mikvah first."
Stories of Tzaddikim and Mikvah
Rebbe Mordechai of Chernobyl zt’l said, "If someone comes to me without first immersing in the mikvah, I can see all his bad deeds, even those he committed behind closed doors. But if he went to the mikvah before coming to me, I don't see anything bad. The mikvah purifies him" (Raza d'Uvda).
Reb Yosef Chaim Sonnenfeld would immerse himself in the mikvah every day, sometimes even twice daily. Reb Isser Zalman Melzer zt'l asked Reb Yosef Chaim Sonnenfeld zt'l why he goes so often. "Wouldn't it be better to learn Torah at that time?" Reb Yosef Chaim Sonnenfeld zt'l replied, "If mikvah can turn a goy into a Yid, imagine what it can do to a Yid!" Reb Isser Zalman said that Reb Yosef Chaim's response changed his perception of mikvah.
Reb Mordechai Pogramansky zy'a was in the Kovno Ghetto during the war. One day, he heard Yidden speaking on the street, bemoaning their lot. Reb Mordechai said, "Rabbosei, listen to me. I have two questions for you, and I know that you will agree with my answers: If a soldier decides to kill some Jews, will his colleagues bring him to court for that?" They answered that nothing would happen to the soldier. He won't even be questioned for killing a Yid. Reb Mordechai moved on to his second question, "So, maybe you can explain to me why he doesn't do what he wants to do? He wants to pour Jewish blood like water, so what stops him? He isn't afraid there will be consequences, so what holds him back from fulfilling his heart's desire? It must be that Hakadosh Baruch Hu is with us, and Hakadosh Baruch Hu tells him, 'No! Don't kill them!' Remember that Hashem is always with us, in these dark times." The men survived the war and said that they always remembered these words. From that day on, they didn't see the soldiers. They only saw Hashem, Who was with them, and decides at every moment what their fate should be.
