Resources used include Lois' Bible reference section, American Bible Society, International Bible Society, Biblehub, John MacArthur (Grace to You), Dr. David L. Cooper (Sept. 1942), and Wikipedia.
The author is anonymous, although either Paul or Barnabas has traditionally been accepted as the author. The overall consensus is that the letter was written primarily to Hebrew Christians (i.e., Hebrew believers, Jewish converts) who were familiar with the Old Testament and who were under intense persecution and in constant danger of returning to Judaism, or at least of attaching too much importance to ceremonial observances. The letter encourages them to persevere in the face of persecution and to not become lax in their commitment to follow Jesus, who was perfect and superior in comparison to anything Judaism and the old covenant had to offer. The author admonished them not to turn away from their only hope of salvation.