In this dissertation, I explore the historical development of Thomas Aquinas's teaching on Christ's grace and wisdom. Through a close reading of thirteenth century texts, I show how Thomas's early thought is best understood against the backdrop of thirteenth-century debates. Thomas's own internal development takes on a character of its own, moving from the Scriptum to the Summa theologiae. I argue that Thomas's development is characterized by an increasing emphasis on the soteriological motivation for the Incarnation. For Thomas, Christ's perfection in grace and knowledge must be understood first and foremost with respect to the grace of headship. This leads to a corollary emphasis, realized more explicitly throughout his career, on grounding every co-assumed perfection of Christ in the human nature rather than deriving them abstractly from the hypostatic union. This reading of Thomas's teaching runs counter to dominating accounts of Thomas's development that anachronistically impose modern categories and concerns onto Thomas's account. The dissertation also pushes back against well-intentioned defenders of Thomas's mature teaching who, in attempting to defend the teaching of Christ's earthly beatific vision, nevertheless end up using arguments that the Common Doctor would likely have rejected. My dissertation highlights the central importance that the humanity of Christ plays in Thomas's understanding of the salvation and the communication of grace. It is because Christ's humanity is the instrument of the divinity and the head of the Church that he must possess, in his very humanity, the fullness of grace and truth, for it is from his fullness that all others receive grace.