It was not the Reformers who came up with the doctrines of salvation by grace and imputed justification, rather, it was God. It was not necessary to critically define and defend these doctrines in the early church since they were accepted as Christian truth revealed by God in Scripture (see http://www.apuritansmind.com/Justification/EarlyChurchJustification.htm for substantiating church father quotes).
The Council of Nicaea in 325 AD was not convened by a pope nor was any important theological issue resolved by a papal decree. Obviously, no one had yet even thought that such an appeal would have final authority over the entire church. The Church of Nicaea did not believe in Marian doctrines such as the Immaculate Conception of Mary, her Bodily Assumption, nor purgatory, indulgences and transubstantiation as currently practiced. These beliefs were added over the ensuing centuries after the Council of Nicaea as a geographical Catholic (universal) Church became a theological Roman Catholic Church.
That these beliefs were not accepted by all is indicated by thirteenth century Roman Catholic inquisitor Reinerius (died 1259) who claimed that more than seventy sects existed outside the Roman Church, many of which were ancient, going back even to the time of the Apostles! In his book, The Pilgrim Church, E. H. Broadbent does an outstanding job demonstrating that some of these sects were what we would not now call bible-believing evangelical Christians. The Reformers came out of the Roman Church and moved doctrinally towards those who were already there, the Waldenses, Hussites and Lollards being the most numerous.
Charles Spurgeon, prince of preachers, states, “We [Baptists or Anabaptists] did not commence our existence at the Reformation, we were reformers before Luther or Calvin were born; we never came from the Church of Rome, for we were never in it, but we have an unbroken line up to the apostles themselves. We have always existed from the very days of Christ, and our principles, sometimes veiled and forgotten, like a river which may travel underground for a little season, have always had honest and holy adherents… Long before your Protestants were known of, these horrible Anabaptists, as they were unjustly called, were protesting for the 'one Lord, no faith, and one baptism.' No sooner did the visible church begin to depart from the gospel than these men arose to keep fast by the good old way.”
Contrary to popular sources there has never been a day since Pentecost when there was no New Testament church somewhere on this earth. Many practiced believer’s baptism, systematic study of the Scriptures and were willing to be persecuted for unpopular, biblical and historic truths.
