What’s the difference between biblical theology and systematic theology? Geerhardus Vos provides some thoughts in his seminal work Biblical Theology: Old and New Testaments:
Biblical Theology occupies a position between Exegesis and Systematic Theology in the encyclopedia of theological disciplines. It differs from Systematic Theology, not in being more Biblical, or adhering more closely to the truths of the Scriptures, but in that its principle of organizing the Biblical material is historical rather than logical. Whereas Systematic Theology takes the Bible as a completed whole and endeavors to exhibit its total teaching in an orderly, systematic form, Biblical Theology deals with the material from the historical standpoint, seeking to exhibit the organic growth or development of the truths of Special Revelation from the primitive pre-redemptive Special Revelation given in Eden to the close of the New Testament canon. (pg. vi)
In other words, the fundamental distinction between the two disciplines is not one of content. Instead, it is of structure and emphasis. Later on, Vos adds:
In Biblical Theology the principle is one of historical, in Systematic Theology it is one of logical construction. Biblical Theology draws a line of development. Systematic Theology draws a circle. (pg. 16)
What’s the difference between biblical and systematic theology? It’s the same content but different intent. It’s the same special revelation but different structure.
Biblical theology tells the storyline of Scripture. Systematic theology applies the storyline of Scripture to the storyline of life.