The writer of Hebrews demonstrated the superiority of the New Covenant to the Old Covenant by demonstrating that the sacrifice of the New Covenant is better than those of the Old Covenant (9:23). The countless sacrifices of the old era though offered over and over could not take away sins (10:4), but Christ’s one sacrifice of Himself was sufficient to take away all the sins of all of His people for all time (9:26-28)!
This argument is continued in Hebrews 10:11-13 taking a slightly different approach. The point of comparison is not between the sacrifices themselves but the high priest who offered them. Every Old Covenant high priest stood ministering daily and offered repeatedly the same sacrifices which could never take away sins (vs.11). But Christ, after He had offered one sacrifice for sins forever, sat down at the right hand of God (vs.12). The contrast is between the Levitical high priest who “stands” and Christ the New Covenant High Priest Who “sat down.” The Old Testament high priest could never sit down because his work was never done! When Christ died on the cross for our sins, He said, “It is finished!” The work of eternal redemption was complete in the one sacrifice of Himself! There were no chairs in the tabernacle, but Christ sat down at the right hand of God after He purged our sins (1:3).