If sola Scriptura is meant to be the guiding principle of Christianity, then why did it take nearly 400 years for the canon of the New Testament to be formally established?

As Protestants, both Matt Swaim and Ken Hensley took for granted that sola Scriptura was the historic Christian rule of faith, but had never really inspected that claim. How is it, for example, that the Nicene Creed, established in 325 A.D., was formalized some 50 years before the official table of contents for the New Testament?

Matt and Ken share what they found when they searched through the history to find evidence for the doctrine of sola Scriptura in the first centuries of Christianity.