The furnishings in the Tabernacle were carefully prescribed – nothing was without a practical and symbolic purpose. Nowhere is it mentioned that there was ever a chair in the Holy Place.
God chose to use the sacrificial system that He gave to Israel as a daily reminder that we are all fallen creatures who need to acknowledge our sin and confess our need for a Savior.
The Aaronic priests would stand in the Temple, day after day, fulfilling their role as mediators between man and God, and the high priest would enter the Holy of Holies once a year and stand before the altar to make atonement for the sins of the people.
They were required to stand because their work was never finished. Animal sacrifices could never take away human sin (Hebrews 9:9–10). If they could, then there would be no point in offering them over and over. The blood of bulls and rams could never take away men's sins, it could only cover sin.
And every priest indeed stands day by day ministering and offering oftentimes the same sacrifices, which can never take away sins: but he, when he had offered one sacrifice for sins forever, sat down on the right hand of God;
Heb 10:11 -12
Christ "sat down" because His priestly work was finally finished.
Christ's sacrifice was made once for all and forever. Through Him our sins are not simply covered but fully forgiven, we can rejoice that the Mosaic Law, the Feasts of the Lord, the priestly ceremonies, and bloody sacrificial offerings of the Old Covenant, were shadows of the glorious reality that was manifest in Christ. Jesus has saved us from our sin.
What’s more, we are to be seated together with Him in heavenly places!
The Holy of Holies was off-limits to everyone except the Great High Priest, and even he could only enter it one time each year, on the Day of Atonement.
God wanted His people to take this seriously – so seriously that two of Aaron’s sons were stricken dead for entering it uninvited. (Leviticus 10)
With a loud cry, Jesus breathed his last. The curtain of the temple was torn in two from top to bottom. Mark 15:37
This temple “curtain”, also translated as “veil”, from the Greek word “katapetasma” was the impenetrable barrier that separated the special “holy of holies” from the rest of the temple.
This physical ripping of the temple curtain when Jesus died symbolized the absolute blasting apart of the barrier between mankind and God!
“Therefore, brothers, since we have confidence to enter the Most Holy Place by the blood of Jesus, by a new and living way opened for us through the curtain, that is, his body, and since we have a great priest over the house of God, let us draw near to God with a sincere heart in full assurance of faith, having our hearts sprinkled to cleanse us from a guilty conscience and having our bodies washed with pure water” (Heb 10:19-22).
We can now approach God’s holiness face to face without fear of certain immediate death. This is possible because the greatest of all Great High Priests accomplished the perfect atonement for sins by his death. He made that temple curtain, and even the entire Old Testament sacrificial system, obsolete.
Jesus sat down -- once and for all!