Hebrews was written to address some of the fundamental misunderstandings that the Jewish people had about Jesus.
This (unknown) author is correcting their ignorance of who Jesus was, and explaining how he completes and fulfils Israel's history, law, ceremonial rituals and priesthood.
And this is highly relevant today. We too can have a wrong understanding of Jesus and his work. We may do things in his name but have become detached from him. We are invited to 'fix our eyes on Jesus'. He is the ultimate and final expression of truth. He is absolutely central in our Christian lives.