Christian observances of Yom Kippur occur when a Christian-style Day of Atonement models itself on the Jewish holiday of Yom Kippur.
In the Roman calendar still observed by Traditionalist Catholics, the Michaelmas Ember days (the Wednesday, Friday and Saturday of the first full week after 14 September (the Feast of the Exaltation of the Holy Cross, or "Roodmas") are penitential days inspired by the Jewish solemnities of the “seventh month,” Tishrei (תִּשְׁרֵי), especially Yom Kippur. Those days' first Lesson (liturgical reading) focuses on the Old Covenant’s Day of Atonement and the fast of the seventh month (Lev. 23, 26-32).[1]
As observed by the Living Church of God and United Church of God:
The Christian Day of Atonement is based on the English translation of the Jewish Holy day Yom Kippur. The day is commemorated with a 25-hour fast by Jews, but normally a 24-hour fast by Christians who observe it. While not observed by the mainstream of professing Christianity, the Christian groups (mostly those with origins in the old Worldwide Church of God) that do observe it usually refer to it as the Day of Atonement...
Generally, the Sacred Name Movement and groups reject Easter and Christmas as pagan in origin and observe the holy days of Leviticus 23 such as Yom Kippur, as well as Passover and the Feast of Weeks.[2]
See main article: Messianic Judaism and Hebrew Christians. Messianic Jewish congregations devote serious effort at presenting a rationale for taking Yom Kippur. Such as by the Emmanuel Messianic Jewish Congregation (Clarksville, Maryland, USA):
Jews for Jesus describes its observances of this day as follows:
Some argue that celebrating this holiday in the Christian faith is redundant in that Christians no longer observe the Day of Atonement since Christ has atoned for all sins once and for all.