 In the third book , Calvin describes how the spiritual union of Christ and humanity is achieved . He first defines faith as the firm and certain knowledge of God in Christ . The immediate effects of faith are repentance and the remission of sin . This is followed by spiritual regeneration , which returns the believer to the state of holiness before Adam 's transgression . However , complete perfection is unattainable in this life , and the believer should expect a continual struggle against sin . Several chapters are then devoted to the subject of justification by faith alone . He defined justification as " the acceptance by which God regards us as righteous whom he has received into grace . " In this definition , it is clear that it is God who initiates and carries through the action and that people play no role ; God is completely sovereign in salvation . Near the end of the book , Calvin describes and defends the doctrine of predestination , a doctrine advanced by Augustine in opposition to the teachings of Pelagius . Fellow theologians who followed the Augustinian tradition on this point included Thomas Aquinas and Martin Luther , though Calvin 's formulation of the doctrine went further than the tradition that went before him . The principle , in Calvin 's words , is that " All are not created on equal terms , but some are preordained to eternal life , others to eternal damnation ; and , accordingly , as each has been created for one or other of these ends , we say that he has been predestinated to life or to death . " 
