In case you're not familiar with exactly what went on in the tabernacle under the old covenant, the author breaks it down for you.
Back in Exodus, God gave Moses the instructions to make a tent. He built it so that God could be properly worshipped while the Israelite people were on their way to the Promised Land (it took a while—forty years to be exact).
Inside the tent there was a lampstand (or menorah), a table, and some bread. The author calls this "the Holy Place."
There was also a curtain or veil that separated out another section of the tent: the Holy of Holies. This was the V.I.P. section that held the Ark of the Covenant. The only person who could ever enter this area was the high priest, and he could only peek in once a year on Yom Kippur. It was very exclusive.
When the high priest went into the Holy of Holies, he took blood from a bull and a male goat. Once inside, he would sprinkle the blood on the Ark of the Covenant (kind of gross, but hey). The idea was that this ritual would help the priest and the people atone for their sins and get right with God again.
Needless to say, the author is pretty critical of all this. He doesn't think these rituals can help bring people closer to God.
What will? According to Hebrews, Jesus. Duh.
See, Jesus was a high priest, but he didn't go into a tent in the desert help people. He used "the greater and perfect tent." That's not something that people made but that the Creator himself made.
Jesus also didn't mess around with animal blood. He went straight for the good stuff and used his own blood to atone for everyone's sins. (Just in case you were wondering why the crucifixion had to be so darn gory.)
When Jesus sacrificed himself, he didn't just purify people's bodies; he also worked his magic on our minds, spirit, and conscience. Now, believers are freed from performing "dead works" and they can put their faith in a God who's alive.
Think of it this way, says Hebrews: Christians are God's kids and they're entitled to inherit all the good things he has. But generally, you can't claim an inheritance until someone dies. So it's kind of like God wrote a will for humanity and then, when Jesus died, we got to cash in.
Bottom line: someone has to die. The author is pretty sure that you need a little blood spilled to start up a new covenant.
After all, when Moses announced God's plan for the people, he sprinkled blood all around the tent and on their holy items.
Clearly, Jesus was just following Jewish law when he died on the cross. Except he did the law one better.
He didn't stroll into some tent in the desert. When he died, Jesus waltzed right into Heaven and put in a good word for all of humanity with the Big Guy.
And while the high priest has to do the same ritual year after year, Jesus' sacrifice was so awesomesauce that he only had to do it once to accomplish the same results.
People only get to set foot on this Earth once, but Jesus will come back. Last time, he sacrificed himself for our sins. The next time he makes an appearance, says the author, he'll save all the people who had faith in him.