The Didache (Koine Greek: διδαχή), also known as “The Teaching,” or, “The…
— Read on www.ancient.eu/Didache/
As the above article indicates, scholars disagree about the date of authorship for the Didache, but scholars do agree external evidences (quotations by Eusebius) show a probability of 4th C.
To me, this accounts for the prescription of a bishop’s monologue/commentary present in the text, a phenomenon known by scholars to have arisen in 4th C Christianity.
On these reasons, I side with the later date for the Didache. It is of use only so far as it gives evidence of the beginnings of a hierarchal, liturgical church. For greater context and further development, search this blog also for mentions of Clement I, Ignatius of Antioch, Eusebius, Constantine & Theodosius I.