Toward the bottom comes this summary:
a study which interprets faithfully something of the past is a good thing. But its significance as a work of theology, defined by the end of theology, will depend a great deal on the extent to which one is also able to clarify its value for the task of affirming the reign of God in the midst of the contemporary situation. Theology is defined by history only while at the same time being defined by the end of history.The issue can be easily framed in terms of Bernard Lonergan's 'functional specialties', an eightfold division of labour. Mind you, such a 'functional' approach in theology can - in our day especially - have the negative effect of legitimizing "theological" inquiry that is not essentially or even tangentially theological. History as "theology", yet all we get is history. To some extent, this position is set in default by departments of Church history - in some denominational colleges and faculties. But church history is not historical theology.
Regarding Historical theology proper, take Lonergan's functional specialty of history (or interpretation). If you assume that the theological task of either interpretation or history (functional specialties #3 and #4 in Lonergan's schema) is something that is autonomous from the larger theological inquiry, then you can end up with atheological interpretation or atheological history. Inasmuch as autonomous interpretation or historical analysis concerns religious material, then we are dealing with Religious Studies...but nothing more.
To some extent, Lonergan conceded the scenario of the independence of Theology from Religious Studies by commenting on the fact that functional specializations 1 through 4 (Research, Interpretation, History, Dialectics) are carried out within Religious Studies. The question that Lonergan - writing in the early 1970's - didn't ask (although he was certainly aware of the cultural impact of a pervasive atheism) is this: what if the constructive question of God (seen through the layered (intellectual, moral, religious) act of conversion) simply drops off the radar screen for interpreters and historians in Theology faculties? What does that bode for institutions of theology? The experience of many departments and faculties in British universities over the course of the past 50 years is instructive, as is the number of formerly religiously committed private colleges and universities in the U.S. But, this and other historical matters would take a set of long paragraphs to unfold...