There was some delay between the writing of the NT documents and their universal acceptance as Holy Scripture (= canon). In fact, the first list to recognize the 27 books of our NT comes from the mid-4th century (see here). The delay feels a bit unsettling, doesn’t it? It shouldn’t, however, for at least three reasons.
First, remember that most of the NT documents were indeed recognized immediately for what they were—authoritative bearers of the gospel. Doubts persisted for only a handful (Heb, Jas, 2 Pet, 2–3 John, Jude and Rev). Second, that some documents took longer to be recognized as Scripture and that others that were later labeled as “non-canonical” were, for a time, read as Scripture should not be terribly surprising. The church, after all, was an international body and, at this point, lacked centralized organization. Transparently, it would take time for documents to spread around—travel was slower then than it is today. And, it would take time for the true character of individual documents to be assessed, especially since the theological savvy of individual communities surely varied. Moreover, if Christian communities could be confused about the reliability of traditions during the apostolic age (see, e.g., 2 Thess 2:2; Gal 1:6–9), is it at all surprising that they could be in subsequent ages? Third, and closely related, is the fact that the important criterion of traditional use demands some delay. As one observer notes, “The force of traditional usage could not come explicitly into play until the third and fourth centuries, by which time the church had some retrospect on its customary practices” (Gamble, “Canonical Formation of the New Testament,” DLNTD 192).
For this and related reflections, see my “Is the New Testament God’s Word?” (Bible and Spade 24.3 : 58–66). And for additional help, see, esp., Michael Kruger’s “Ten Basic Facts about the NT Canon Every Christian Should Memorize.”