Harnack, Adolf. “Prolegomena, § 5. “Die Gemeindezustände. Zeit und Ont der Διδαχή.” pp. 88-170. Die Quellen der Schrift.” Lehre der Zwölf Apostel. Leipzig, J.C. Hinrichs, 1884.
“I. Die Organisation der Gesammtkirche und der Gemeinde nach der Διδαχή unter Vergleichung der anderen Urkunden.” “1. Die Christenheit oder die Kirche.” pp. 88-93.
Harnack observes that the Didache never specifies any one community but rather speaks of Chrsitianity as if it is addressing a universal whole (Harnack 1884, 88). This attitude is similar to that of Tertullian, who views Christianity as a body joined by a particular faith and unified practice. Harnack considers both Tertullian and the Didache to describe a relatively universal form of Christianity, as opposed to a localized form (Harnack 1884, 89). The text of the Didache even speaks to numerous life situations common to all, from instruction to baptism, to prayer, reception of the Sacrament, Christian living in the community, and finally an eschatological hope.
Harnack recognizes that unity of the faith does not always indicate uniformity of practice (Harnack 1884, 90). The idea of a guest-friendship, for example, may be carried out in different ways according to needs and abilities. Harnack also sees a variety of practices which, while considered Christian, may have more tendencies toward Enthusiasm, different views of order and worship, and differing approaches toward community life (Harnack 1884, 92).