John Gerstner: The church always taught "Sola Fide" implicitly, and the Reformers explicitly defended the doctrine against apostate Romanists

John Gerstner explains the history of "Sola Fide" within the church:

One may say generally of the history of the doctrine of justification that solafideanism (justification-by-faith-alone-ism) was taught implicitly, but not explicitly, from the beginning of the church. That is, it was known in the early church that salvation was by faith alone, but not until the sixteenth century was the church called upon to define that teaching more precisely. Those in the church who had quietly apostasized opposed this essential truth (adherents of Tridentine Roman Catholicism), while the faithful (Protestants), affirmed it. The Reformers defined and refined the doctrine in the fires of controversy. (Dr. John Gerstner, History of the Doctrine of Justification)