In the fourth century the Church came to use the word “canon” to refer to the authoritative body of Holy Writings that defined the rule of faith and practice among Christians. Originally, “canon” referred to a straight rod or bar that could be used for various purposes such as a carpenter’s rule or the beam of a balance. In most instances the idea of rule or norm or model was involved. Athanasius (about 296–373), bishop of Alexandria, appears to be the first to apply the word “canon” to the books accepted into the New Testament, in contrast to apocryphal books that were rejected.
By the end of the first or the beginning of the second century, a collection of Paul’s letters apparently existed; it is referred to by the author of 2 Peter 3:16. Clement of Rome (about 95) refers to Paul’s Letter to the Corinthians and makes allusion to several others. Ignatius of Antioch (died about 110) alludes to several of Paul’s letters.