The cleansing in the real service in heaven must be accomplished with the blood of Christ. “Without shedding of blood there is no remission.” Remission, or putting away of sin, is the work to be accomplished. LF 172.4
But how could there be sin connected with the sanctuary in heaven? We can find the answer by looking at the symbolic service, since the priests on earth served in “the copy and shadow of the heavenly things” (Hebrews 8:5). LF 172.5
The ministry of the earthly sanctuary consisted of two parts. The priests ministered each day in the Holy Place, while once a year the high priest performed a special work of atonement in the Most Holy, to cleanse the sanctuary. Day by day repentant sinners brought their offerings. They placed their hands on the victim's head, confessed their sins, symbolically transferring the sins from themselves to the innocent sacrifices. The animals were then killed. “The life of the flesh is in the blood” (Leviticus 17:11). The broken law of God demanded the life of the transgressor. The priest carried the blood, representing the life of the sinner whose guilt the victim bore, into the Holy Place and sprinkled it in front of the veil, behind which was the law that the sinner had broken. This ceremony transferred the sin symbolically to the sanctuary. In some cases the priest did not take the blood into the Holy Place, but then he ate the flesh. Both ceremonies symbolized the transfer of sin from the repentant sinner to the sanctuary. LF 172.6
This was the work that went on throughout the year. The sins of Israel were transferred in this way to the sanctuary, and a special work became necessary to remove them. LF 173.1