All men are required to immerse in a mikvah (ritual pool) on the day before Yom Kippur. In certain communities, women also immerse in a mikvah on this day.
There are two reasons for this immersion:
- In order to be ritually pure in preparation for the holiest day of the year.
- The immersion is symbolic of conversion. Just as a convert immerses in a mikvah and thus becomes a "new person," so, too, it is our intention to do teshuvah (repentance) and become new people.
In many chassidic communities it is customary for men to immerse in the mikvah three times on this day. Once before the morning prayers, once before the afternoon prayers, and then again after the final meal, immediately before Yom Kippur.