Authorship. A considerable variety of opinions on this subject has been advanced from the earliest times. From around 400 A.D. to 1600 A.D, the author was traditionally considered to be Paul. However, the epistle makes no internal claim of authorship, which is inconsisten with the rest of Paul's epistles.
In addition to Paul, some have suggested Paul's companion Silas, Pope Clement I, Luke, or some unknown Alexandrian Christian. Two leading candidates are Barnabas, first suggested around 300 A.D, or Apollos, first suggested by Martin Luther. Modern scholarship has reached no strong consensus. The letter has, however, always been accepted as part of the New Testament canon.
Initial text from Easton's Bible Dictionary, 1897 -- Please update as needed
To whom addressed. Plainly it was intended for Jewish converts to Christianity, probably for the church at Jerusalem.
Its design was to show the true end and meaning of the Mosaic system, and its symbolical and transient character. It proves that the Levitical priesthood was a "shadow" of that of Christ, and that the legal sacrifices prefigured the great and all-perfect sacrifice he offered for us. It explains that the gospel was designed, not to modify the law of Moses, but to supersede and abolish it. Its teaching was fitted, as it was designed, to check that tendency to apostatize from Christianity and to return to Judaism which now showed itself among certain Jewish Christians. The supreme authority and the transcendent glory of the gospel are clearly set forth, and in such a way as to strengthen and confirm their allegiance to Christ.
It consists of two parts: (a) doctrinal (1-10:18), (b) and practical (10:19-ch. 13). There are found in it many references to portions of the Old Testament. It has been regarded as a treatise supplementary to the Epistles to the Romans and Galatians, and as a kind of commentary on the book of Leviticus and Temple worship in general. Its constant reference to Temple worship has been used to date the epistle before the destruction of the Temple (A.D. 70), but that is not conclusive.