The Book of Hebrews contains a lot of theology. It begins by exploring the question of just who Jesus is. Remember that the first generation of Christians had a lot of questions and uncertainties regarding their faith. Was Jesus the greatest human being who ever lived - or was He something more? Could He possibly be considered on a par with the angels?
The book's author (whose identity is known only to God) is determined to demonstrate that Jesus, as the Son of God, ranks far above even angelic creatures.
While angels are divine servants, Jesus Himself is divine!