This is a subsidiary post of The Formation of the New Testament…from Beginning to End.
Various factors were at work in the multi-century process that culminated in the 27-book New Testament canon. Here are some of them:
The Writings Themselves
The geographic separation of congregations receiving the writings (and, possibly, collections thereof)
See Metzger, 1987, p 13
Proliferation of Christian literature: good (orthodox, edifying) and bad (heresy, pseudepigrapha); particularly the rise of literature falsely attributed to the apostles.
The gradual dissipation of oral tradition (i.e. vibrant and full in the beginning, waning with each generation) (diminishing utility over time)
The “Gentilization” of the church: i.e., the transition from Jewish leadership to Gentile leadership. (This would also have the effect of hastening the evaporation of oral testimony since the Gentiles lacked the social structures and practices upon which the Jews had long relied to preserve oral tradition.
The broader political environment (e.g. before and after Constantine)
Periods of persecution, especially for possession of sacred writings
Gamble comments on the Constantinian environment and what it did for canonization in The Canon Debate, loc 6410-6435
The intra-church environment (e.g. before and after Council of Nicea)
Degree of inter-church communication (incl. sharing of literature)
The developing technology of book production
See profound paragraph p 67 of TNTC by Gamble
See Ch 2 Books and Readers by Gamble
See ch in Christian Artifacts by Hurtado
See ch 27 in The Canon Debate – “The Greek NT as a Codex” by Daryl D. Schmidt
See my exchange with Larry Hurtado on his blog
Dayton, Wilber T. “Factors promoting the formation of the New Testament canon” in Bulletin of the Evangelical Theological Society 10.1 (Winter 1967): 28-35.
Farmer, William R. “A Study of the Development of the New Testament Canon” in The Formation of the New Testament Canon: An Ecumenical Approach by Farmer and Farkasfalvy. Paulist Press, 1983, 89 pages. See p. 8, 29-34.