The High Priest had many duties and responsibilities, but his most important duty was to minister on the Day of Atonement. The Day of Atonement occurred on the tenth of Tishri, which is the seventh month on the Hebrew religious calendar. This corresponds to the Gentile months of September-October. The Day of Atonement is also known as the Day of Forgiveness. The Jews call it Yom Kippur. The Day of Atonement is the most solemn of all days. This is the day for making atonement or covering for the sins of the entire nation of Israel.
