Well, embracing the true doctrine of the Gospel, that a person is justified by God's grace through faith, and not by works would be paramount.
But you know, there is no evidence that the early Church ever actually believed that idea specifically. Nor, conversely, is there any evidence that they did not, because the early Church did not talk that much about justification; rather, their position was one where salvation was by grace, through faith, but also entailed salvific works.
Now, ecumenical reconciliation between Lutherans and other churches is possible on this issue, based on the idea that when St. James the Just wrote “faith without works is dead,” the good works could be seen as the result of a living faith that was salvific rather than hypocritical. Whereas someone who did have a living faith, but was rather a hypocrite, would not be expected to produce good works, but rather would engage in evil deeds consistently due to their hypocrisy.
I regard this as possible, since the Orthodox position clearly makes faith a prerequisite - there is no disagreement on the point that salvation is by faith. After all, John 3:16 says as much, and we also have the Good Thief. And since Lutherans are sacramental, obviously it is not the case that baptism or the Eucharist would be seen as works, nor the process of enrolling as a catechumen (Orthodoxy maintains that if a catechumen dies before baptism, they are still saved, and I believe Rome asserts something similiar, the Baptism of Desire). And furthermore, we believe that if someone is martyred, that constitutes the Baptism of Blood, and we disagree with the Roman Catholics, in that while they do regard that as salvific, we regard it as instantly glorifying, so if an Orthodox Christian is martyred (whether Eastern or Oriental), they become a saint instantly.
Now, the reason why I am talking about Orthodoxy in this context, is because it is obvious that the sequence of events that led to the decline of the Papacy into the state of corruption that prompted Martin Luther to initiate his reforms began in the late 7th century when the Roman church began to doctrinally drift away from the Eastern Orthodox Church; the symptoms of this were masked for a time by Roman resistance to iconoclasm, which endeared Rome to iconodule bishops in the East who were fighting the Iconoclast heretics who had managed to seize control of the Church of Constantinope. But following the Triumph of Orthodoxy, immediately there followed the Filioque Controversy, which was the first in a series of major cracks that began to appear, and these resulted in a rupture of communion, with the Patriarch of Constantinople being excommunicated by Rome in 1054, and the Patriarch of Antioch being excommunicated in 1078, and then the crusades happened, in which Eastern Orthodox and Oriental Orthodox Christians were in some cases cannibalized by crusaders in the First Crusade, and in all of the Crusades, the Orthodox suffered, but none moreso than the Fourth Crusade, which was supposedly raised to attack the Holy Land, but which was diverted by Venice to attack and conquer the Byzantine Empire, which the Venetians regarded as a threat to their power. And this, along with the West predicating military assistance to save the Empire from Turkocratia, on the acceptance of the Council of Florence, which the laity rejected less than a hundred years before the Lutheran reformation, simultaneously with the reformation in Prague under St. Jan Hus and St. Jerome of Prague, who are venerated as martyrs by the Orthodox Church, was really the last straw.
By the way the last bit I think is important. Since Moravian theology was close to Lutheran theology, at least until it was corrupted by the radical Pietisim of Count Zizendorf, the fact that the founders of the Moravian church are regarded, at least by the Orthodox Church of the Czech Lands and Slovakia, as martyrs, I think bodes well for the prospect of reconciliation.
But what I would not want to see would be a scenario where the Pope of Rome embraced a Lutheranism that was incompatible in its expression with Orthodoxy, because all this would do is continue the East-West schism, and it would also likely alienate more Catholics than if the Pope merely embraced Orthodoxy, since Rome has in recent years made a point of praising our theology extensively and publically as part of the process of ecumenical reconciliation (cynically, I would say it was partially done in the hope that perhaps the Antiochians would have agreed to merge with the Melkites, and more than that, to prop up the Eastern Catholic Churches and discourage conversions from Eastern Catholicism to Eastern and Oriental Orthodoxy.
