Let's take a walk in Hebrew chapter 10 starting in verse 4
For it is not possible that the blood of bulls and of goats should take away sins. Wherefore (because it is not possible that the blood of bulls and goats could take away sin) when he (Christ) cometh into the world, he (Christ) saith, Sacrifice and offering thou wouldest not, but a body hast thou prepared me (the Word was made flesh): In burnt offerings and sacrifices for sin thou hast had no pleasure. Then said I (I the writer or us for that matter. For we were made to be in HIS image and likeness), Lo, I (we) come (in the volume of the book (the human instruction manuel, the Bible) it is written of me,) to do thy will, O God. Above when He (HE being Christ) said, Sacrifice and offering and burnt offerings and offering for sin thou wouldest not, neither hadst pleasure therein (Because there was a constant rememberance of sin every year because they could never take away sin vs.3 so neither has HE had any pleasure in); which are offered by the law; Then said he (Christ), Lo, I come to do thy will, O God. He taketh away the first, that he may establish the second (purging our conscience (who we are, our inner man), a sanctifying to the purifying of the flesh from dead works (the taking away of sin, dead works, acts the cause death) to serve the Living God. Moreover he sprinkled with blood both the tabernacle, and all the vessels of the ministry. And almost all things are by the law purged with blood; and without shedding of blood is no remission. It was therefore necessary that the patterns of things in the heavens should be purified with these; but the heavenly things themselves (us) with better sacrifices than these. Heb 9:14,13 21-23)
By the which will we are sanctified (purged conscience, a sanctifying to the purifying of the flesh from dead works, the taking away of sin to serve the Living God) through the offering of the body of Jesus Christ once for all. And every priest standeth daily ministering and offering oftentimes the same sacrifices, which can never take away sins (purge our conscience, who we are our inner being) : But this man (Christ), after he had offered one sacrifice for sins for ever, sat down on the right hand of God; From henceforth expecting till his enemies be made his footstool. For by one offering he hath perfected for ever them that are sanctified. Whereof (to this perfectedness) the Holy Ghost also is a witness to us: for after that he had said before, This is the covenant (perfectedness of them that are sanctified) that I will make with them after those days, saith the Lord, I will put my laws into their hearts, and in their minds will I write them;
(Heb 10:4-16 KJV)