[T]wo problems with the discipline [of New Testament Theology] have repeatedly emerged as most significant.
The first problem, it is said, is an unhealthy blend in the discipline of dogmatics with historical concerns. On the one hand, theological convictions influence New Testament theologians both in the conclusions they draw about the meaning of the New Testament texts and in their insistence on examining only the canonical documents. On the other hand, since the church values these documents largely for the historical claims made in them, New Testament theologians find that they must work as historians in much the same way that any historian would work with ancient texts. Is it possible to bring together faith and reason in this way, or must New Testament theologians bracket their own dogmatic presuppositions about the importance of the New Testament and place the canonical texts on a level with all other ancient texts? If so, then they should shift their attention away from the theologically biased investigation of “New Testament theology” to the more objective and universally useful task of describing the history of early Christian thought.
The second problem arises from the theological diversity of the New Testament texts. The New Testament documents not only express a variety of theological themes, but sometimes they speak in different ways on the same theme. Do these differences sometimes amount to contradiction? If not, why is the theological coherence of the New Testament sometimes so hard to detect? If so, is it accurate to speak of “New Testament theology” at all, as if we are speaking of some coherent whole? (Frank Thielman, Theology of the New Testament: A Canonical and Synthetic Approach, Grand Rapids: Zondervan, 2005, pg 19)
Good things to consider and questions that must be answered when beginning a study of biblical theology or New Testament theology.