The Importance of Luther's Understanding of Justification

Luther had a strongly extrinsic alien kind of imputation um understanding of justification because that would seem to be an important fracture point right where we have inherent righteousness versus an extrinsic righteousness. Luther came round to that even though I don't think that was how Luther himself initially thought of it so he would say that it solidifies during the 1520s and then in effect it's picked up by other reformers like Calvin. By about 1540 something like that it really has become a defining feature of the Reformation movements a whole, one of the things I would love to investigate but I don't know how this happened is how did that idea crystallize and become normative?