Schaff, Philip. "Ch. 32: Lessons of the Didache." The Oldest Church Manual Called the Teaching of the Twelve Apostles. Second Edition, Revised and Enlarged. New York: Funk & Wagnalls, 1886, 138-140.
As he sets out to summarize the lessons of the Didache, Schaff says "its value is historical and historical only, but this is very considerable, and exceeds that of any known post-Apostolic document" (Schaff 1886, 138). He places it in the transitional period of 70-150.
The lessons we learn primarily fall into twelve categories, which I summarize with Schaff's numbers.
1. Church membership requires catechesis.
2. The catechesis was moral and practical.
3. The morality taught was of a very exacting nature.
4. Baptism was the approved initiation.
5. Eucharist and Agape were combined every Lord's day.
6. No sacrament other than baptism and eucharist is found.
7. The Lord's Prayer was used three times daily.
8. The Lord's Day was celebrated as a feast, while Wednesday and Friday were fast days.
9. Apostles and Prophets brought the Gospel, while Bishops and Deacons governed the church.
10. Much of the New Testament was known mostly from living teaching.
11. Little was mentioned of Christ or the Apostles outside the Gospel tradition.
12. Christians held an eschatological hope.