Since the New Testament is a document of history, specifically of the history of religion, the interpretation of it requires the labor of historical investigation. The method of this kind of inquiry has been worked out from the time of the Enlightenment onward and has been made fruitful for the investigation of primitive Christianity and the interpretation of the New Testament. Now such labor may be guided by either one of two interests, that of reconstruction or that of interpretation—that is, reconstruction of past history or interpretation of New Testament writings. Neither exists, of course, without the other, and they stand constantly in a reciprocal relation to each other. But the question is: which of the two stands in the service to the other? Either the writings of the New Testament can be interrogated as the “sources” which the historian interprets in order to reconstruct a picture of primitive Christianity as a phenomenon of the historical past, or the reconstruction stands in the service of the interpretation of the New Testament writings under the presupposition that they have something to sat to the present.
Theology of the New Testament, 2.251.
Bultmann concludes this paragraph by indicating that in his NT Theology, the historical task is at the service of interpretation.