Justifying grace is for Kant the way religion symbolizes, in terms of our relation to God, our hope to overcome the propensity to evil through the change of heart. Divine forgiveness does not abolish or transcend morality but occurs in accordance with morality. The Son of God symbolizes as vicarious atonement our moral receptivity to God’s mercy. The sacrifice of Jesus Christ on the cross is the way Christianity symbolizes it in revealed religion. For Kant rational religion includes faith in God’s justifying grace. It does not include prevenient or sanctifying grace but does not exclude these either. They are religiously acceptable parts of revealed Christianity, but their reality and our need for them lie beyond what pure reason can know. Some critics claim that Kant’s account of divine grace is inconsistent with itself. But closer examination shows that it is self-consistent, and for Kant rational religion is even consistent with Augustinianism about grace, while neither affirming nor denying it.

Chapter 2 argues that Thomas’s mature view of the formal cause of original justice created an unresolved problem for his doctrine of original sin. Though his early writings sharply distinguished the rectitude of the human will in the state of original justice from supernatural sanctifying grace, by the mid-1260s (e.g., STh I, q. 95, a. 1) he implied that the formal cause of original justice is sanctifying grace. The problem is that Thomas also held (1) that Adam should have been the principal cause of original justice in his posterity and (2) that no creature can be the principal cause of sanctifying grace. Thomas’s mature view implies that the disposition to original justice never could have been sexually transmitted. This implies that his account of original sin as a whole needed to be modified. Adam’s failure to transmit the disposition to original justice rendered the lack of original justice sinful in his posterity: if Adam couldn’t have done this in the first place, how could his descendants have original sin?