Biblical Theology is a discipline of exegetical theology, one of the 4 that are part of what is called the “Encyclopedia of Theology” – Exegetical, Historical, Systematic, and Practical Theologies (Hagenbach).
Biblical theology is considered by some to be the capstone of exegetical theology. However, it is not exegetical theology itself.
The reason for calling it the capstone is because it presupposes everything else within exegetical theology. To be clear, this means it is keeping in mind the Hebrew and Greek behind our modern translation, historical context, textual criticism, translation approach, the history and canonicity of the Bible, and hermeneutics. Everything done within exegetical theology is taken into account when engaging in biblical theology studies.
Biblical theology is, therefore, the area of theology of the entire Bible. It looks at the Bible as a whole and does not subdivide based upon Old Testament and New Testament. As a result, it naturally traces the entire story of the Scriptures in which you can see God’s progressive revelation.
Now, I do want to point out that biblical theology is not practiced in every corner of Christianity today. There are many who would do everything else found within the exegetical branch and then ignore the capstone and/or use the term biblical theology in an entirely different way – usually to state whether or not a particular theology or theological approach is biblical. With this in mind, the use of the term “biblical theology” can often seem unclear.