However the concepts have been filtered through the concerns of later Christian theology. From at least the time of Augustine of Hippo in the 5th Century, "righteousness" has been seen as a moral and religious quality. In the Roman Catholic model, Christians are transformed by God's action, developing a righteousness of their own. In the 16th Century, the Protestant Reformers came to understand human acceptance by God according to a "forensic" model, in which God declares humanity not guilty, even though they were in a moral sense still guilty of sin. However, the Reformers continued to accept the traditional concept of righteousness. What changed is that the righteousness was seen as Christ's, which was credited ("imputed") to Christians by God.