Why is the book of Hebrews named that? The book of Hebrews in the New Testament shares a name with the Hebrew people of the Mosaic Law. Why was that book named Hebrews?
It's called that because it was written as a letter to Hebrews.  Most of the Epistles are titled after the group they were written to.  (Corinthians was written to the Church at Corinth, etc.)

From http://christianity.about.com/od/newtestamentbooks/a/Book-Of-Hebrews.htm


  Date Written:
  
  Hebrews was written before the fall of Jerusalem and the destruction
  of the Temple in 70 A.D. Written To:
  
  Hebrew Christians who were wavering in their faith and all future
  readers of the Bible.


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