The Lutheran and Reformed traditions share a common root in the Protestant Reformation, but the relationship has been something of a sibling rivalry. The debates were perhaps most acrimonious in the 16th and 17th centuries, but the present climate could be described as cold and isolated. On the Reformed side at least, theologians rarely engage with Lutheran positions and critiques. Caricatures exist on either side and so a greater clarity of the debates—and common root—is needed. One such example is the theological approach to assurance of salvation.
This paper presents a clarifying comparison of the two approaches with the headings of a receptive and sacramental piety (Lutheran) and a practical and interior piety (Reformed). These categories help elucidate not only the theological battles fought between the traditions but also within each tradition. But even here clarification is needed. A historical investigation shows that the chasm has widened over time such that one can see a deeper similarity in the 16th century. This is especially true from the Reformed perspective.
Further attention will be given to the paradoxical role that the possibility of apostasy plays within concepts of assurance. Lutheran theology allows for the possibility of apostasy, yet it is the Reformed tradition which has struggled most with assurance. Since the author is Reformed and not Lutheran, the conclusion of the paper suggests ways that Reformed can learn from Lutheran formulations, with the possibility of both clarity and mutual edification.