The writer, in pressing home his point, has been contrasting the old and the new covenant and showing how superior the new is to the old, with a better Mediator.
The old order of worship took place at the tabernacle, the tent that was designed and laid out by divine order. It was established by a fleshly commandment, indicating that it was only temporary, not permanent.
At the centre of the tabernacle was the Most Holy Place. Only the High Priest could enter, and he could only do that once a year, on the Day of Atonement. The Ark of the Covenant was within the Most Holy Place, standing for the presence of God.
The Lord Jesus Christ did not enter a tabernacle made with hands. He entered heaven itself, not an ornate tent. Nor did he rely on the sacrifice of animals to enter there. Rather, the blood that He shed was His own. It can cleanse the conscience and effects a deeper work on the soul. Hold fast then to the sacrifice of the Lord Jesus Christ, our Saviour and Redeemer.