The plain truth is that false doctrine has been the chosen engine which Satan has employed in every age....Unable to prevent the Fountain of Life being opened, he has laboured incessantly to poison the streams which flow from it....False doctrine soon overspread the Primitive Church after the death of the Apostles....False doctrine in the middle ages so completely overspread the Church, that the truth as it is in Jesus was well nigh buried or drowned. During the last three centuries before the Reformation, it is probable that very few “Christians” in Europe could have answered the question, “What must I do to be saved?”....False doctrine since the days of the Reformation has continually been rising up again....
J.C. Ryle, Warnings to the Churches, 1877