No one had ever sat down before.
For generations, men entered the temple to make sacrifices. In dark, smoke-filled rooms, full of the smell of incense and blood, men stood.
J. Alex Kirk astutely commented on an earlier blog post that there was nowhere for the priest to sit in the tabernacle. The High Priest's job was never done. There was always more to do, more sacrifices to make, more, more, more.
Hebrews 8 pauses to note that Jesus sat down.
The Christological vision of the author of Hebrews sees Jesus' work as finished. He is the Great High Priest, the one who made a once-for-all sacrifice, submitting himself to death, even death on a cross.
And he sat down. The only place to sit in the tabernacle, in the temple, was the throne of God. And only God could sit on that throne.
We needed a priest and we needed him sit, we needed him to finish the work of our salvation. We needed him to sit down.
So he sat down.