Packer on Justification

“Martin Luther described the doctrine of justification by faith as articulus stantis vel cadentis ecclesiae — the article of faith that decides whether the church is standing or falling. By this he meant that when this doctrine is understood, believed, and preached, as it was in New Testament times, the church stands in the grace of God and is alive; but where it is neglected, overlaid, or denied, as it was in medieval Catholicism, the church falls from grace and its life drains away, leaving it in a state of darkness and death. The reason why the Reformation happened, and Protestant churches came into being, was that Luther and his fellow Reformers believed that Papal Rome had apostatized from the gospel so completely in this respect that no faithful Christian could with a good conscience continue within her ranks.