Schaff, Philip. History of the Christian Church (The Complete Eight Volumes in One). Amazon Kindle Edition, 2014.
Volume 2, Ante-Nicene Christianity A.D. 100-325, “Chapter 13. Ecclesiastical Literature of the Ante-Nicene Age, and Biographical Sketches of the Church Fathers.” sec. 159-204.
§ 167. Barnabas.
After a somewhat extensive bibliography, Schaff points out that the Epistle of Barnabas, which makes no mention of the author’s name or location, speaks to the reader as a peer, not as a teacher (Schaff 2014, loc. 20964). The letter begins with 17 chapters of a doctrinal nature, then continues with four chapters which are more akin to practical exhortation. Schaff considers the writing and message inferior to that of Hebrews, though similar in its thrust (Schaff 2014, loc. 20972). The view of the Old Testament and of Judaism articulated in Barnabas is allegorical and to be interpreted mystically. Schaff finds in Barnabas an ideal of pure spiritual worship and a dietary law that had nothing to do with eating and drinking but everything to do with the people with whom we associate (Schaff 2014, loc. 20979).
Schaff does consider Barnabas to have some redemptive qualities, though. He does have a zeal for knowledge and confirms major elements of the gospel (Schaff 2014, loc. 20994). He refers to several passages from the New Testament, as well as the Old Testament.
Barnabas was considered by Clement of Alexandria and by Origen as a genuine work of Barnabas, who toured with Paul (Schaff 2014, loc. 21002). Others, such as Eusebius and Jerome question the authority but not the authorship. On the whole, Schaff considers it not to be a genuine work of Barnabas and not to bear authority (Schaff 2014, loc. 21010). Schaff is “quite certain that if Barnabas wrote this epistle, he cannot be the author of the Epistle to the Hebrews, and vice versa” (Schaff 2014, 21017). Schaff speculates that the letter was probably written by a Jewish convert, familiar with allegorical methods, written between 70 and 100.