Scholars differ widely in their analyses of book fifteen. Does Augustine’s intended argument finally fail? Is the humility with which Augustine concludes his work evidence of a learned ignorance? Does the love of God comprehend and move Augustine’s entire treatise? These and similar positions make up the summary views of Augustine’s De Trinitate. This paper suggests that Augustine’s argument ends by completing the purpose with which he began. Book fifteen presents the mind turned toward God in a participation of sapientia. By means of a precise dialectic, governed by the authority of Scripture, the mind as imago trinitatis approaches the Trinity with confident humility. Augustine finishes the entire work with a prayer as the summit of sapientia in dialectic.