Customs for Erev Rosh Hashanah (the day leading up to) include the recitation of longer than normal Selichot prayers and the omission of Taḥanun in the Morning and Afternoon Services (SA Orach Chayyim 581:3).
In addition, most synagogues change the Torah mantles and the parokhet, the curtain that hangs before the Ark, to white ones in honor of the High Holidays.
Similarly, it is customary to wear a white robe, often called a kittel, during services on the High Holidays and especially on Yom Kippur. White symbolizes purity and thus exemplifies the worshiper’s desire to achieve atonement and forgiveness.
There is a custom of immersing oneself in the mikveh (also written mikvah) before Rosh Hashanah (BT Rosh Hashanah 16b), although some suggest it should be done just before Yom Kippur.
As in the case of immersion in a mikveh before a wedding, or as part of a couple’s intimate life together after marriage, the mikveh is a means of personal purification and therefore perfectly suited to the spirit of spiritual purification and internal preparation before the High Holidays.
Some have suggested that immersion in the mikveh is a model of personal rebirth: just as one emerges from the watery environment of the womb into a new world, so too does one emerge from the purifying waters of the mikveh into the world reborn.
The use of the mikveh teaches us that life constantly gives us chances to begin anew. That is certainly the optimistic message of the High Holidays, and a visit to the mikveh at this time of the year merely reinforces that message.
Adapted with permission from The Observant Life.