Harnack, Adolf. “Prolegomena, § 4. “Die Quellen der Schrift.” Lehre der Zwölf Apostel. Leipzig, J.C. Hinrichs, 1884, pp. 63-88.
Speaking to the source of the text, Harnack immediately sings its praises, particularly in originality. He considers it far and away the best and oldest example of extracanonical literature of early Christianity (Harnack 1884, 63). Haarnack catalogs references in the Didache to the Old Testament, to the overall ideas of the Gospel, to the letter of Barnabas, and to the Shepherd of Hermas (Harnack 1884, 65). It seems to Harnack that the references to New Testament ideas but not texts suggest knowledge of traditions but not of a defined New Testament canon. This could reasonably push the author to give such detailed explanations of both doctrine and practice to the readers (Harnack 1884, 66). Harnack provides a detailed list of passages with references to other works of early Christian literature (Harnack 1884, 66-68). He follows it with a chart of statements from the Didache in parallel columns with the synoptic gospels and with other early witnesses (Harnack 1884, 70-76). Of the 23 segments, Harnack observes that 17 are dependent on Matthew’s Gospel (Harnack 1884, 76). Many are related to Matthew and nothing else. Harnack proceeds to speak about each segment and its comparisons to other passages in turn. While Harnack sees a clear relationship between the Didache and Matthew, he also sees a close relationship with the Episle of Barnabas (Harnack 1884, 82), especially in its moral teaching. Harnack goes into some detail, specifically and frequently comparing passages in chapter 19 of Barnabas. It is interesting, though addressed almost as an afterthought by Harnack, that no Pauline letters are referred to in the Didache (Harnack 1884, 87). There are certainly many topics which are common to both Pual and the Didache, but here is no evidence of interaction. Harnack does provide a list of passages which would lend themselves to comparison (Harnack 1884, 88).