Chapter 5: This chapter talks about how Jesus is the Great High Priest. This chapter also says that God said that Jesus is a priest forever in the order of Melchizedek. In the end it talks about how you need to know the elementary truths of God's word just like an infant drinks milk.
Chapter 6: In the start the author says that we should go on from elementary teaching to maturity. And then it tells us not to be lacy but to imitate those with faith and patience.
Chapter 7:At first the chapter talks about Melzhizedek who was the king of Salem. It talks about how he blessed people lesser than him. And then it talks about how Jesus is holy, blameless and pure priest.
Chapter 8: This chapter talks about that we have a high priest who is the right hand of God. And then it talks about what high priests are supposed to do and that Jesus is Superior to them.
Conclusion: These chapters tell us a lot about Jesus as our high priest and that we should be mature.