Yom Kippur, The Day of Atonement, has significant theological importance in the New Testament. The book of Hebrews (Chapters 8 to 10) argues that Yom Kippur foreshadowed Christ’s work as priest. In the OT, “the high priest went alone once a year, not without blood, which he offered for himself and for the people’s sins committed in ignorance,” (Hebrews 9:7). Christ, however, “came as High Priest of the good things to come, with the greater and more perfect tabernacle not made with hands, that is, not of this creation. Not with the blood of goats and calves, but with His own blood He entered the Most Holy Place once for all, having obtained eternal redemption,” (Hebrews 9:11-12). The author of Hebrews understands Christ’s redemptive work to be the fulfillment of this sacrificial ritual of the Day of Atonement.”
That Christians might celebrate this day is fine, such only that it is identified and grounded in the perfect and completed work of Christ. The confession of our sins against God and neighbor, whether intentional or not, and the seeking to reform and conform our lives more and more into the image of Christ is a rightful part of our sanctification. We do not await a single day to make amends, but we struggle daily to put off the old man and the flesh. The Christian is free to do this in prayer anytime or more properly within the worship of God at church.
Jews believe this day gives them a fresh start or a clean slate of sorts. We Christians, on the other hand, are assured that our sins are not counted against us, because the one sacrifice of Christ has abolished in one act what the repetition of this ceremony could not and cannot do.