Raith's sustained comparative study of Aquinas and Calvin on Romans focuses on the believer's participation in Christ. Recent Calvin scholarship has brought “participation” to the fore (e.g. Todd Billings), showing there is a robustness to Calvin's thought about the believer's union with Christ, permeating through a number of theological images. This union, expressed in justification, makes Christian believers one with Christ through the work of the Holy Spirit. Justification is forensic, emphasizing the imputation of Christ's righteousness to the believer who is “clothed” in Christ's justice. Justification is distinct, but related to sanctification in Calvin—a duplex gratia. In sanctification, believers can do good works, which have no “merit” in themselves, but are only “good” by Christ's merit and action.

In comparison and contrast, Raith examines Aquinas's writings on Romans to reveal what is in his view is a more fully “participatory” activity for believers. This is what the Council of Trent called a “transformational righteousness” which sees a place for works in justification. While emphasizing throughout that Aquinas's teachings on justification harmonized with Calvin's focus on God's unmerited forgiveness of sins and imputation of Christ's alien righteousness, Raith says Aquinas sees justification in participatory terms which means “the transformation of the sinner into a just person” (57). Justification is a state and a process for Aquinas. God's justifying work occurs in and through the sinner, in contrast to Calvin who saw Christ's work as occurring for and to the sinner (54). For Aquinas, God's forgiveness of sins, occurring sola gratia and sola fide non merito, “brings the believer into a participatory relationship with Christ's own justice” so that “faith is not the ‘grasping’ of a justice that always remains in a sense alien to the believer, but rather faith is the justification of the mind through grace that enables the individual to participate in Christ's justice according to the believer's own mode of existence” (58).

For Calvin, there is a sharp dichotomy between “justification by faith” and “justification by works.” If humans were to be justified by “works,” they would have to keep the whole of God's law. Because of sin, they cannot obey the law perfectly. In justification, the righteousness of Jesus Christ is given to sinners by faith. So for Calvin, says Raith, “our relationship to God rests on something extra nos” (207). Raith's work is to show that this principle of the clash between justification by faith and justification by works occurs throughout Calvin's exegesis of Romans and, in the end, does not foster the intimacy of relationship with God that is found in Aquinas's theology. Raith argues that for Calvin, “in the end we are not brought into the deep, intimate relationship with God that recent emphases on participation seek to recover. Those who follow Calvin's theology continue to evidence his nonparticipatory framework in their own thinking” (207).

In justification, Christ's alien justice “becomes residential in Aquinas's perspective, transforming the sinner into a just Christian, while it remains extra nos for Calvin” (211). “Our righteousness,” for Aquinas, is “a participation in Christ's righteousness; good works do not contribute to establishing our peace with God.” But, good works do occur “solely within a relationship of peace with God.” God enables the believer to keep the law, to do good, truly meritorious works (58), as an expression of God's favor, bestowed in justification. Obedience to God's law for Aquinas, says Raith, sees obedience “as a gift of God establishing his people to participate in his work of salvation—his work of making his people happy in him” (213). This means that “obedience within justification does not need to be conceived as a human striving to gain God's favor, but rather it should be understood as God's favor—his favor toward sin-enslaved human beings, enabling them to be free in Christ's grace.” This enables Aquinas to retain “a place for works in our justification” (214).

The burden of Raith's book is to examine Aquinas's and Calvin's exegesis of Romans (1:16b-8:18) comparatively and find areas of agreement and disagreement. The focus in all chapters is on participation. The two parts, following the flow of Romans, are “Participation in Christ's Justification” and “Participation in the Spirit's Transformation.” In the first, Raith examines justification, Abraham, and peace with God, which are also the chapter titles. In Part II, there are two chapters on the Spirit's work of transformation, and then “Life in the Spirit,” before the conclusion.

Ultimately, Raith does not believe Calvin's theology, especially with its interpretations of Romans 6 and 7, is adequate to account for the “no condemnation” of Romans 8:1. Raith says a main difference relates to the way the healing work of Christ's grace effects the sinner: “Aquinas believes that both the debt and ‘stain [macula]’ of sin are totally removed through union with Christ, while Calvin argues for the removal of the debt but only the partial and ongoing removal of the macula” (131). For Aquinas, believers participate in their own perseverance: “we actually and truly persevere and remain faithful to the end” (216). Human obedience is “intrinsic to obtaining the inheritance” (217). Calvin in his critique of Trent “denies that justification has anything to do with a ‘quality’ within the believer and seeks to keep the justice by which we are just before God extra nos” (210). This view of Calvin, believes Raith, ultimately hinders true participation.

Raith's study clarifies two approaches at the nub of Reformation controversies. But does the “participation” motif in the Aquinian mode do full justice to the kind of concerns Calvin had in maintaining a “differentiated union” (3; citing Billings) which distinguishes Creator and creature in union with God; and the ongoing power and extent of human sin? Must Aquinian “participation” define what “participation” must be? Is this definition the appropriate category by which to judge Calvin? These questions need further discussion.