[I]t should be clear that we cannot simply lump all the books of the New Testament together indiscriminately and use them as a quarry for the stones, which we shall use to build our edifice. It would be possible to create a compilation of theological statements from the New Testament that has nothing more than a harmonizing assembly of quotations taken at random from any of its books. Such an approach would wrench the statements out of their contexts and lack the careful examination of their nuances to establish precisely what they were intended to affirm and imply. It would also assume that the quotations will all necessarily reflect the same point of view. But is a collection of texts a theology? There has to be some kind of arrangements. If so, how does one decide how to group the texts? To create a building rather than a cairn it is necessary to have some kind of plan or design.
Consequently, the first approach cannot in practice be separated from a second, accompanying tendency. This is to take over an existing plan such as is found in a textbook of systematic theology without any firm evidence that this framework was in the minds of any of the New Testament authors. However, it has to be said that people who do this are usually quite convinced that their framework is that of the New Testament.
Two errors of method thus come together in this combination of approaches, the indiscriminate use of the books of the New Testament as if they all necessarily reflected identical thinking, and the use of a later framework as if it were that of the New Testament. The result can be distorting and anachronistic. (I. Howard Marshall, New Testament Theology: Many Witnesses, One Gospel (Downer’s Grove: IVP, 2004), p. 24-25)