Christians prior to the councils mentioned by the other posters were not completely clueless as to which books were to be received; there were earlier lists. One such earlier list of unknown authorship is the* Muratorian Fragment*, which dates to between A.D. 150 and 200. Though the beginning and ending portions of its listings are now missing, still in the part that now remains, it mentions nearly all of the books that are in our New Testament. It begins with mention of Luke as the third gospel and John as the fourth gospel. (Matthew and Mark are presumed to have been mentioned in the now missing beginning portion of the Fragment.) It then mentions, but not necessarily in this order, the Acts of the Apostles, thirteen of Paul’s letters (Romans, 1 & 2 Corinthians, Galatians, Ephesians, Philippians, Colossians, 1 & 2 Thessalonians, 1 & 2 Timothy, Titus, and Philemon), two of John’s three letters, Jude, and John’s Apocalypse (Revelation).
The surviving portion of the Muratorian Fragment does not mention Hebrews, James, 1 & 2 Peter, and one of John’s letters.