The forgiveness of sins, on the one hand, is presented as an objective reality for Christians. Jesus Christ, the God-man, accomplished redemption through his life, death, and resurrection, and the Holy Spirit applies that to those who trust in him. Yet life is messy. And the history of the doctrine of forgiveness underscores that the subjective element has rendered it difficult for the church to articulate this doctrine in such a way that covers the varied experience of individuals. Said another way, sinners plagued by guilt for their wrongdoing often cannot escape the doubts they have about whether or not they are truly forgiven. This question, then, is by no means merely metaphysical. Rather, it bears directly on the daily lives of individuals, and it arguably touches the life of every human being who has the capacity to feel shame.
In considering the question of the forgiveness of sins, I picked up an old book by Cambridge theologian William Telfer, The Forgiveness of Sins: An Essay in the History of Christian Doctrine and Practice (Philadelphia: Muhlenberg, 1960). While the book has its shortcomings, it nonetheless presents a valuable discussion of how Christians have understood the doctrine of forgiveness and practiced it throughout history.