Discussing the concept of the will as man’s fundamental feature, a concept profoundly shaped by Augustine’s Confessions, Charles Trinkaus points out the very different use of Augustine’s ideas which Renaissance writers such as Petrarch fostered, which differed greatly from Augustine’s own:
although he remained marvellously aware of the personal and spiritual elements of religion, in his subsequent career as a Churchman [Augustine] created an objective theological structure and an ecclesiastical programme that was to endure for centuries. The more intense and sensitive medieval ecclesiastics, for instance Bernard of Clairvaux or Bonaventura, always could rediscover the subjective depths of religious feeling in St. Augustine but for the most part his great influence over the medieval centuries was through the structural and doctrinal elements of his writings. It was with the Italian humanists that Augustine’s great spirituality was again comprehended, but this time without the ecclesiastical context with which he objectified and surrounded his deep personal insights. [In Our Image and Likeness: Humanity and Divinity in Italian Humanist Thought Vol. 1 (The University of Chicago Press, 1970), pg. 20]
In other words, long before the Reformation, the force of a much more personal-moral and will-oriented Christianity found in Augustine was unleashed by the Italian humanists in direct contrast to the more bureaucratic-scientific and reason-oriented approach of the Church hierarchy. Note that while this represented to some extent a modification of Augustine, it nevertheless came from Augustine. And note also that this is all part of a massive and systematic change taking place on all fronts of culture, with no one able to see how it was going to turn out. Medieval blends almost seamlessly into Renaissance, and Renaissance blends almost seamlessly into Reformation, Augustine modifies Augustine, and in the confused and exciting and oh so very human jumble very few can be accurately said to be “Black Hats” or “White Hats.” This story isn’t about Truth Vs. Error, Light Vs. Darkness, the Gospel vs. the False Gospel, Christ’s One True Apostolic Bureaucracy Vs. Individual Heretic-Rebels Wielding Private Judgment, or any of the other vain, shallow caricatures of developed post-16th century polemical traditions. God almost always seems to work in ways much more mysterious than that.