Yom Kippur, the Day of Atonement, is the most solemn day on HaShem's calendar. It falls on the tenth of Tishrei, ten days after Yom Teruah. The root kaf-peh-resh means to cover, to ransom, to atone (see the keyword entry for Kapparah). On this day, and only on this day, the Kohen Gadol entered the Most Holy Place, passed through the veil, and sprinkled blood on the kapporet, the golden covering of the Ark. The entire nation fasted, afflicted their souls (Leviticus 23:27), and waited for the High Priest to emerge alive. If he emerged, atonement was made. The breach between HaShem and Israel was covered for another year.

The writer of Hebrews builds his entire argument on Yom Kippur. Yeshua is the Kohen Gadol who entered the heavenly tabernacle, not with the blood of goats and bulls, but with His own blood, and obtained eternal redemption (Hebrews 9:12). He did not enter a man-made Holy of Holies. He entered the real one, the one the earthly tabernacle was patterned after. And He did not need to come out and go back in every year. He entered once, for all, and the atonement He secured does not expire. The veil that separated the people from the presence of HaShem tore when Yeshua died (Matthew 27:51). Yom Kippur ended. Not the concept of atonement, but the annual repetition. The covering is permanent.

The KJV, ESV, NASB, and NIV mention the Day of Atonement in Leviticus and reference it in Hebrews, but they rarely help the English reader see that the entire argument of Hebrews 7-10 is a Yom Kippur exposition. Without the feast as your framework, Hebrews reads like abstract theology about priesthood and sacrifice. With the feast, Hebrews reads like a guided tour of what happened when the real Kohen Gadol walked through the real veil with real blood and came out the other side with permanent atonement in His hands. The feast is the commentary. Remove it and you are reading the conclusion without the argument.