What's the point of all this high priest talk? Well, just that Christians have the best high priest possible. One who's "seated at the right hand of the throne of Majesty in the heavens." NBD.
See, the Jewish high priests in the old days worked in the tabernacle (the tent that God instructed the Israelites to assemble in the desert after the exodus from Egypt). They had to offer gifts like rams and goats to atone for their sins and follow Jewish law while doing it.
But Jesus works in the "true tent." That's not a place set up by people, but by God himself. We guessing it's pretty snazzy.
He's in charge of a better covenant with way better promises, says the author. If God's first stab at a covenant with his people had worked, there wouldn't be any need for Jesus. But it didn't, so it's on to Plan B.
The author quotes the prophet Jeremiah and explains that God himself told the people that one day he would make a new covenant with them.
This new deal wouldn't be like the old one. God planned to write his law on their hearts, not on parchment. People wouldn't have to tell each other about God—they'd just know him.
Needless to say, the author pretty much thinks that this is what God has done with Jesus. The old covenant is out and the new one is in.