The Patristic Period
One of the earliest concerns of the Christian church, beginning with the apostles and intensifying through the patristic and medieval periods, was that those who profess the Christian faith should live in a way befitting their profession of faith. In the apostolic and patristic periods our theologians were often writing within a hostile culture to converts from paganism. There was much that Christians could not control: what the pagans thought of them (e.g., they drown babies, they were cannibals, they were a burial cult etc). The Greco-Roman pagans seemed determined to try to force the Christians to conform outwardly to Greco-Roman piety. They were happy to add Jesus to the pantheon but they (and the non-Christian Jews) were greatly troubled by his crucifixion and they could not tolerate the notion that he had claimed (and the Christians confessed) that he is the only way to God. There offended too by the Christian doctrine of the Trinity as unreasonable and others were critical of the claim that Jesus was born of a Virgin. Occasionally, in the patristic periods, there were even sporadic outbreaks of government-sponsored persecution intended either deal with the problem of the Christians. Those pogroms failed and the Christians persisted. One thing the Christians could control, one claim the Christians could make was that their behavior was exemplary. Those who investigated the Christians from the outside reported (e.g., Pliny the Younger c. 112 AD) that the Christians covenanted among themselves not make false oaths, not to steal, not to desire the belongings of others etc. They recited the Ten Commandments in their services. As part of their apologetic (i.e., defense of the faith) Justin Martyr and Tertullian repeatedly challenged the pagans to find anything wrong with the way Christians behaved. Christians, they argued, were good citizens and could sustain any trial to which the pagans might put them. They repeatedly begged the authorities to leave the Christians alone so they could pursue their lives peacefully.
The Medieval Period
Beginning in the late Patristic period and continuing through the medieval period, however, the high Christian doctrine of the moral and apologetic necessity of good behavior morphed into something else: part of the ground and instrument of the Christian’s standing before God, part of the ground and reason of their final salvation from the wrath to come. By the high middle ages (e.g., as reflected the teaching of Anselm. Bernard of Clairvaux. and Thomas Aquinas) it was widely held, though never formally confessed by the church, that salvation is by sanctification and that sanctification is by grace and free cooperation with grace. The mainstream doctrine became that Christians needed to accumulate merit and that was that free will, i.e., the un-coerced act of the will was essential merit. Behind this lay a set of philosophical assumptions that were received more or less uncritically, chief among which was the notion that God can only say “righteous” or “sanctified” if the Christians is actually, inherently, intrinsically righteous and sanctified. Particularly in the West and entire doctrine of salvation (soteriology) was established to explain how that was and what one must do to be saved (sanctified and therefore justified and finally delivered from the wrath to come).
The became that Christians are infused with a sort of medicine (a metaphor frequently used for grace) which produces new life (there is nothing new about sovereign, prevenient grace) with which the Christian must cooperate toward the formation of a kind of merit that has intrinsic worth. The medieval theologians called this “condign merit.” They recognized, however, in different ways that our cooperation with grace is imperfect or that our good works are still imperfect (different writers put it differently) and therefore God must impute perfection to our best efforts. They called this congruent merit. There was a widespread conviction that the only way to promote sanctity (holiness) and obedience among Christians is to suspend their final standing before God (salvation) upon their cooperation with grace. Good works were not evidence of a right standing with God and salvation but essential to the ground and instrument of our justification and salvation. Where at least some of the Fathers had spoken of justification and salvation by grace through faith in something like the way the Protestants would later do, the medievals defined faith rather differently. They defined faith as sanctification. They taught that faith is a virtue, that it has intrinsic power, and that it is “formed” in us through sanctification, i.e., by grace and cooperation with grace. Where Paul had written, “faith working through love” (Gal 5:6) the medievals (e.g., Thomas) taught “faith formed by love.” They spoke of the “theological virtues” of 1 Corinthians 13: faith, hope, and love. Faith was thought to be the gift of God but it does not given to us fully developed. We must nurture it and since love (caritas from which we get charity) is the greatest virtue, we must develop it by our free cooperation with grace toward the formation of faith. Thus, for the medieval theologians, faith is not so much trusting in Christ and looking to Christ but rather a measurement of the degree of love formed within us, a measurement of our actual sanctity and inherent righteousness.
This prevailing medieval doctrine of salvation by grace and cooperation with grace, however, left the Christian in a state of suspension. Assurance was regarded as ordinarily impossible for the ordinary Christian and undesirable. Indeed, the notion of that one might have certainty that one was saved and would be saved from the wrath to come was regarded as presumption, as arrogance and that was an indication that one was not sufficiently sanctified. Christians were intended in a state of uncertainty. In at least one Saxon Augustinian monk that crisis created by the medieval system would produce a revolution in Western theology, piety, and practice.
When Luther rebelled against the medieval doctrine of justification and salvation by sanctification he re-defined justification as God’s unconditional declaration of justification (righteousness) on the ground of Christ’s condign merit imputed to believers and that received through faith alone (sola fide). Faith in justification and salvation was redefined as the sole instrument through which Christians receive God’s grace and Christ’s righteousness. This is why the sola of sola fide was so important. Love was said to be the fruit and evidence of justification and salvation. Grace was also redefined. Luther and the Protestants found that the medievals had departed from the biblical definition of grace as God’s free favor toward sinners and had turned it into a medicine. They found that some of the Fathers and many of the medievals had downplayed the effects of sin so as to be able to teach our ability to cooperate freely with grace. They recaptured St Paul’s and St Augustine’s doctrine of sin and its deadly consequences.
Where the medievals had come to teach that Christ’s life, death, and resurrection made it possible for Christian to do his part, if he would, Luther and the Protestants declared that the gospel is that Christ had accomplished salvation once-for-all and that he freely distributes it to all who believe, that faith is a free gift of grace, and that even though we are never fully, inherently sanctified or righteous in this life nevertheless we are already fully justified before God and saved from the wrath to come. We are simultaneously righteous even though we remain actually sinners (simul iustus et peccator). That was something that virtually no medieval theologian could say and it was flatly contrary to what became formal Romanist dogma in the mid-16th century.
What of sanctification? Whereas the medievals made sanctification the instrument of our justification and salvation Luther and the Protestants taught that our actual, progressive sanctification is the necessary consequence of our justification and our salvation from the wrath to come. Like the Fathers and the medievals they believed and taught the moral necessity of holiness and obedience to God’s moral law (the ten commandments) but unlike the medievals they taught Christian obedience to the law is the fruit of our justification and evidence of our salvation. There were those, particularly in the 1550s, who dissented from the Protestant consensus. One theologian (Osiander) taught that God accepts us on the basis of our union with the indwelling Christ. Another tried to wedge in the medieval doctrine, by teaching that good works were more than evidence but this revision was universally rejected. The overwhelming consensus among Reformed theologians by the mid-16th century was that sanctification is the necessary consequence of our justification and the evidence of our salvation.