The tension between Augustinian determinism (grace) and Pelagian agency (will) did not resolve in the 5th century; it became the primary fault line of the Protestant Reformation and the subsequent Catholic Counter-Reformation.
Martin Luther was an Augustinian priest. His doctrine of Sola Gratia (Grace Alone) was, in many ways, a radicalization of Augustine's late-stage fight against Pelagius. Luther's belief in the total depravity of man—the idea that the will is bound and cannot choose God on its own—is a direct descendant of the "hardened" Augustinianism developed in the Pelagian controversy.
The Counter-Reformation (Council of Trent) attempted a delicate balance, affirming the necessity of grace (Augustine) while maintaining the necessity of human cooperation in salvation (a softened Pelagianism).
Thus, the 5th-century struggle between a North African bishop and a British monk provided the intellectual architecture for the religious wars of the 16th century.
The link between Augustine and Martin Luther is more than just a shared monastic order. It is a shared metaphysical crisis. Luther’s "Tower Experience"—his realization that the "righteousness of God" is not a standard we meet, but a gift we receive—is essentially a rediscovery of late-stage Augustine.
Luther took Augustine's fight against Pelagius to its logical extreme. If the will is truly "bound" (as Augustine argued), then any attempt by the Catholic Church to suggest that "good works" contribute to salvation is, in Luther's eyes, a return to the "heresy" of Pelagianism.
Ironically, the Catholic Counter-Reformation's response was to move back toward a more balanced, "Early Church" view—ironically mirroring some of the very points Pelagius had made 1,100 years earlier: that while grace is necessary, the human person must still consciously cooperate with that grace. The circle of diversity in ancient Christianity thus became the cycle of conflict in the modern era.
The influence of these ancient debates extends far beyond the Reformation. The "Augustinian Trap"—the idea that humans are born with a fundamental flaw (Original Sin)—became the dominant psychological framework of the West for a millennium. It created a culture that viewed the human body and sexual desire as inherently "shameful" or "broken."
The Enlightenment (17th-18th century) can be seen as a massive, belated "Neo-Pelagian" rebellion. When thinkers like Rousseau argued that "man is born free, and everywhere he is in chains," they were essentially reviving the Pelagian claim that human nature is fundamentally good and that "sin" is a product of a corrupt society, not a corrupt soul.
Thus, the dialogue between Augustine and Pelagius is the dialogue of the modern mind: Are we inherently flawed beings in need of an external savior, or are we autonomous agents capable of self-perfection? The "diversity" of ancient Christianity was not a series of errors, but the birth of the primary tension of Western identity.