The New Testament, as understood within the Catholic intellectual tradition, affirms that Jesus of Nazareth is the unique universal mediator of salvation for the human race. At the same time, the Catholic Church affirms that Christ lived and died so that salvation might be offered to all human beings, including those who have no immediate access to baptism or to the fulness of the means of salvation, in the visible Catholic Church. This essay seeks to understand these affirmations by recourse to the theology of Thomas Aquinas. What is his conception of redemption and of the universal efficacy of the passion and merits of Christ? How does his conception of grace provide an indication of the ways God might work in the lives of persons who are not baptized? How are the lives of those who receive grace oriented by inward transformation toward the recognition of significant moral and theological truths? These questions are explored in this essay by recourse to key texts in the mature corpus of Aquinas as well as by consideration of modern and contemporary Thomistic literature.