Heb 10:8-18 Above when he said, Sacrifice and offering and burnt offerings and offering for sin thou wouldest not, neither hadst pleasure therein; which are offered by the law; (9) Then said he, Lo, I come to do thy will, O God. He taketh away the first, that he may establish the second. (10) By the which will we are sanctified through the offering of the body of Jesus Christ once for all. (11) And every priest standeth daily ministering and offering oftentimes the same sacrifices, which can never take away sins: (12) But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God; (13) From henceforth expecting till his enemies be made his footstool. (14) For by one offering he hath perfected for ever them that are sanctified. (15) Whereof the Holy Ghost also is a witness to us: for after that he had said before, (16) This is the covenant 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; (17) And their sins and iniquities will I remember no more. (18) Now where remission of these is, there is no more offering for sin.
Under the Old Testament (Verse 9 – take a way the first refers to the Old Testament which is represented by the Law) the blood of bulls and goats was shed when Israel sinned against God. The problem was that this blood was insufficient to take away sins (Heb. 10:1-8). But under the New Testament (Verse 9 – to establish the second refers to the New Testament which is represented by Grace) there was a single offering that completely and finally once for all time removes sin from those that are sanctified, positionally. This positional sanctification describes a set of people (saints) who have been set apart from sin for the service of God and given a continuing and permanent sinless position before God thru the shed blood of the superior sacrifice, Jesus Christ.
This sanctification could not be provided and sins could not be forgiven with out the shedding of blood from a better sacrifice than that of bulls and goats. So God Himself (the Son of God) came down to earth, put on flesh, dwelt among us, shed his blood and died on curl cross for our sins, was buried and rose again the third day to provide forgiveness to the saints. Because Christ is the superior sacrifice, there is no need to have any more blood sacrifices or offerings for sin. In this we find that the Old Testament (Law) is fulfilled by the New Testament (Grace) which is Christ; and with the work of salvation complete, the saints simply rest in the work of the redeemer, Jesus Christ.