In 1976 Dr. Richard B. Gaffin, Jr., published a programmatic article on "Systematic Theology and Biblical Theology," building especially on the work of Geerhardus Vos and John Murray. Much has happened since then in developments in biblical theology. So I propose to reassess the present-day possibilities for biblical theology's relation to systematic theology.Read the whole article. (You can also read Gaffin's article from 1976 online.)
Here's the last paragraph:
In the end, one of the best arguments for not conforming systematic theology to a single "structural" model deriving from NT biblical theology is that Paul's own example counts against it. In addition to stability in his adherence to truth, Paul's exhibited flexibility in his mode of delivery of the truth. Therefore it is surely permissible for systematic theology to do the same. Biblical theology and systematic theology both need robust interaction with one another for the sake of deepening their methodological and doctrinal soundness. But each may legitimately adopt a variety of structures in communication, and not feel bound to copy in its macrostructure the structures typical of its companion.