If you wear a tallit and tefillin, and blow shofar and keep kosher, but use your Judaism to undermine the right of the seven million Jews who live in Israel to choose their own destiny: Come back. In attacking your own people, you have gone further than those who renounce all traditional observance.

This understanding that we needed to repent and reform was not confined to any particular religion: We Americans of all faiths, or no faith, used to proclaim days of repentance as a nation, especially in times of trauma. During the observance of Yom Kippur, our Jewish brothers and sisters remind us of the high duty of admitting, “I am a sinner.”

At sundown this Friday, Jews across the world will begin Yom Kippur when they will fast and reflect on wrongdoings from the last year.

Yom Kippur, the holiest day of the year in Judaism, begins at sundown on Friday. Here's what the Jewish holiday honors and how it is celebrated.

Considered the holiest day of the Jewish calendar, Yom Kippur is the culmination of a 10-day period of repentance and reflection, which began last week with the start of Rosh Hashanah. This year's events come with a particularly somber tone amid heightened turmoil in the Middle East.