Throughout the Middle Ages, the Western church was discussing and debating the nature of justification. The reformers really believed that the popular (and, by the mid-sixteenth century, official) Roman Catholic position was self-salvation. By "Roman Catholic," I don't mean what's going on at your local Catholic church today. Rather, it is to the medieval position that I refer, the Roman Catholic theology that was represented in the Council of Trent in 1545-1563. What then were the medieval positions on this doctrine?
Thomas Aquinas, the great Catholic theologian of the mid-thirteenth century, had a doctrine of justification, but for him it was just one doctrine among many (Aquinas makes this point in his Summa Theologiae 1-2, q. 113). Somewhere tucked behind, around, and under such subjects as regeneration, predestination, and sanctification was his position on justification. It was a doctrine of justification that involved God loving the sinner insofar as he or she was not a sinner. He did not love the sinner as sinner; how could a holy and just God love a sinner? But he loved sinners insofar as they had the potential to not be sinners.
Another Catholic theologian, John Duns Scotus (who lived in the early fourteenth century), spoke of the necessity of an absolutely selfless act of contrition (sorrow) and love for God by natural means if a person was to be saved. Think about that for a moment. At least once during your life, you would have to perform an utterly selfless act that had no vested interest for you whatsoever, or you would not be saved. Luther believed that this way of justification prevented God from befriending publicans and sinners, and that if it were true, God was not truly free.
Of course, there were many other views, but the medieval consensus that won out has come to be known by the technical name semi-Pelagianism (from the late fourth- to fifth-century debate between Augustine, defender of grace, and Pelagius, a monk who denied original sin and, therefore, the need for supernatural grace). While the Synod of Orange (a.d. 529) condemned both Pelagianism and semi-Pelagianism, the heresy of works-righteousness, erected on the foundation of free will, grew increasingly popular among the masses and even among theologians.
What the reformers said of the position was that it was by necessity a theology of doubt, of fear, and finally of despair of ever being saved. One had to be sanctified enough first in order to merit justifying grace, and the essence of justification was a real change within the human heart. Justification, in mainstream Roman Catholic theology, is primarily a real, empirical change in the human heart. Aquinas argued that justification involves a gradual change from unjust to just, thus justified. Grace amounts to an infused power to lead a God-pleasing life, to cooperate with the Spirit, to gradually move oneself from the category of "ungodly" to that of "righteous." And this would be evident in fewer and fewer sins by the believer. Luther, however, did not agree that the word grace in the Bible means an infused power to live a God-pleasing life, as though grace were a substance. He said rather that grace is the opposite of merit: unmerited favor. We are saved by God's graciousness to us. God has decided to be gracious to sinners; we are saved by his graciousness.
Grace is not even a principle. It is an attribute, a disposition, of the living God. He is gracious. To be saved by God's graciousness is to give up on merit, or to use Luther's phrase, to "let God be God." Luther believed that to let God be God is to recognize that it is he who does the saving, and part of what is requisite in that is for us to quit trying to do the saving. The Roman Catholic position was that God and the believer working together can save, whereas the Reformation position insisted that God can save sinners only if they stop trying to save themselves. The cause of God's graciousness to sinners is not our faith, the reformers insisted; the cause of God's graciousness to sinners is his graciousness. In other words, we do not leverage the love of God out of heaven. We do not have an Archimedean point for a lever to pry it down toward us. Our openness, our yearning for him, our longing to be part of his gracious plan-none of this justifies; none of these dispositions or desires on our part can pry open the gate of heaven.
If the reformers were correct in interpreting what Paul was getting at in his Epistle to the Romans, 100 percent of our salvation is due to God's graciousness, and zero percent is due to anything in us. The Reformation's answer to the question, "Do I contribute anything to my salvation?" is, "Yes, your sin!" The value then of saving faith is only a value in virtue of the object grasped. Faith itself has no virtue; it connects us to the One who is virtuous.