Q. What is the Didache?
A. Several books were highly regarded in parts of the early Church — so much so that some local churches read from them publicly in Mass as if they were Scripture — yet were not included in the final biblical canon by the universal Church. Among these would be such books as the Didache (or “Teaching of the Twelve Apostles”), the Epistle of Clement, the Shepherd of Hermas, the Wisdom of Solomon, the Acts of Peter, the Acts of Paul, the Apocalypse of Peter, the Epistle of Barnabas, and the Gospel of the Hebrews. Some of these books make for more edifying reading than others.
For example, the Didache, written perhaps as early as a.d. 60, gives us a fascinating glimpse into life in the churches of the first generation of Christians. The Epistle of Clement (a.k.a. 1 Clement) is full of godly instructions for Christian life from Pope St. Clement I, written perhaps as early as a.d. 70 by a man who had known St. Peter and other apostles. (Both of these books were composed before the last of the books in the New Testament canon.)
On the other hand, the Acts of Peter (probably dating from a century after the books just named) provides entertaining tales of St. Peter that can sometimes stretch our sense of credulity. In one anecdote, for example, the book claims that St. Peter spoke to a smoked tuna hanging in a window and raised it back to life, so that it swam around in a pond and ate bread crumbs! With God all things are possible, of course, but it may be that the Church rejected this book from the canon because of such stories as these.
The Apocalypse of Peter claims to report what Jesus showed Peter about the end of the world and the torments of hell. In fact, it’s the earliest of the so-called Christian “tours of hell,” books that purport to describe the tortures of the damned in detail. (The most famous book in this genre is Dante’s Inferno.) The Church most likely rejected this “Apocalypse” because Church leaders came to realize that it was not in fact written by St. Peter but was composed much later. Nevertheless, it exerted tremendous influence among Christians over the notions of hell and the end of the world that later developed.
Other books from this period and later, such as the so-called “Gospel of Thomas” and “Gospel of Mary,” were influenced by the heresy called Gnosticism. These were not read as Scripture in orthodox churches and never seem to have been seriously considered for the canon by Church authorities. They may make for interesting reading, but they should not be viewed as reliable sources of Catholic teaching or early Christian history.