Systematic theology will ask questions like "What are the attributes of God? What is sin? What does the cross achieve?" Biblical theology tends to ask questions such as "What is the theology of the prophecy of Isaiah? What do we learn from John's Gospel? How does the theme of the temple work itself out across the entire Bible?" Both approaches are legitimate; both are important. They are mutually complementary.
We should be surprised that a matter that generally plays such an important part in the life of man has hitherto been almost entirely disregarded by philosophers, and lies before us as raw and untreated material.