bro to understand Hebrews look to the Law, leviticus is a major key
concerning hebrews 7:27 its referring to the aaronic preisthood where arron needed to sacrifice foirt for Himself, and then for the people. check out leviticus 16 and really the whole Law when hebrews isnt jiving, it truly reveals the meaning of Hebrews, because Hebrews is a contrast between the new testament, and the old. it shows us how Jesus has fulfilled the priesthood, only in the order of the heavenly melchezidek of the bred and wine, and that aarons preisthood was only temporary, the shedding of the animals blood only a pattern.
when the people sinned sins that werent punished by death, each year the atonement was made and in order for aaron to enter the holy of holies where the glory of God was above the ark, he had to sacrifice each year for himself and then the people. Jesus sacrifice was once for all time. this doesnt mean were already forgiven, but that our forgiveness now, is in the order of melchezidek ( Jesus ) Hebrews 7:12 "
For the priesthood being changed, there is made of necessity a change also of the law.
were under Jesus priesthood in the order of melchezidek, so therefore our forgiveness isnt to sacrifice spotless animals, but ours is given in the gospel by our priest Jesus " i desire mercy, not sacrifice"
we forgive others like our priest taught, and His sacrifice is sufficient, if we do not forgive others, its as if were under the Law and refusing to offer the required sacrifice. Our sacrifice is to follow the gospel, " be merciful and you will receive mercy, forgive and you will be forgiven, give and it will be given unto you" the priesthood changed when Jesus spoke " repent for the kingdom of Heaven is near" He began giving the true Law of spirit, the witness for us, rather than against us. notice how contrary the gospel is to the mosaic Law. its because its a whole new order. the High order of Melchezidek in the time before the mosaic law ever was, based on the faith of abram.
Leviticus 16:2-6 "
And the LORD said unto Moses, Speak unto Aaron thy brother, that he come not at all times into the holy place within the vail before the mercy seat, which is upon the ark; that he die not: for I will appear in the cloud upon the mercy seat. 3Thus shall Aaron come into the holy place: with a young bullock for a sin offering, and a ram for a burnt offering. 4He shall put on the holy linen coat, and he shall have the linen breeches upon his flesh, and shall be girded with a linen girdle, and with the linen mitre shall he be attired: these are holy garments; therefore shall he wash his flesh in water, and so put them on. 5And he shall take of the congregation of the children of Israel two kids of the goats for a sin offering, and one ram for a burnt offering. 6And Aaron shall offer his bullock of the sin offering, which is for himself, and make an atonement for himself, and for his house.