Which of the following statements is true about St. Augustine's writings?

St. Augustine's writings are indeed significant for their inclusion of a defense of original sin. He articulated the concept of original sin as part of his theological framework, particularly in works like "Confessions" and "The City of God." This idea centered on the belief that all humans inherit a sinful nature due to the Fall of Adam and Eve, and it was foundational for his understanding of salvation and grace.

His emphasis on original sin illustrates the broader themes of his work, where he blends theology with philosophical inquiry and personal reflection. This multifaceted approach shows that while his writings cover various topics, the defense of original sin is a critical component that shapes his theological contributions to Christian thought.

In contrast, the other options do not accurately represent the scope or nature of St. Augustine's writings. His work is not exclusive to theology, as it also encompasses philosophy, ethics, and personal memoir. They are not purely historical accounts since Augustine often intertwined his theological insights with historical narratives. Lastly, his writings were primarily in Latin, not Greek, which marked a significant aspect of the Latin Christian tradition.