If we are interested in studying the New Testament (NT) to determine what makes up NT Theology, what sources should be our primary focus? Some traditions suggest that Tradition or ecclesiastical leaders (bishops, presbyters, etc.) should share equal ground with Scripture when we theologize.
Despite the difficulties related to determining the authority of such extra sources and beyond illustrating the problems of having other sources beside Scripture, I. Howard Marshall gives us five reasons to exclude as primary all sources but the twenty-seven NT documents (New Testament Theology, pp. 18-20):
(1) The generation of Christians who came after the NT authors recognized that the NT documents were Scripture in the same way that the Jews recognized the nature of the Hebrew Scriptures. Marshall writes,
“… the fact that a consensus developed concerning them strongly supports the view that the early church was right to recognize that they had certain characteristics, which indicated that they formed a unity.”
I think we also find an example of this in the NT itself. The early church simply was following what began in the writings of the apostles. Consider 2 Peter 3:15-16, where the author connects the writings of the apostle Paul to the “other Scriptures.” Peter clearly had the Hebrew Scriptures in mind and begins to make a strong case for the authority of such a connection. Paul himself noted the authority of his own writings several times (cf. 1 Cor. 14:37).
(2) The NT documents were composed by people closest in time (and relationship!) to Jesus and the events recorded in the NT. This, for Marshall (and myself!) provides the “basis for seeing a possible unity in the relatively limited area and time within which they were composed.”
(3) With the possible exception of several documents (1 Clement; Didache), “the New Testament documents constitute virtually the whole of the surviving Christian literature of the first century.”
(4) There is a unity of concentration found in the NT documents: the NT focuses its attention on Jesus Christ’s life, ministry, death, and resurrection as well as the religious movement that was founded upon these historical events. Marshall acknowledges that this does not necessarily imply that there are no contradictions or that they all say the same things, but that “a corpus of writings with the same central theme must constitute a legitimate object of study.” I mine as well clarify that I do not believe there are any contradictions.
(5) The NT documents have such a high quality of Christian writing that they must be given primary source. Though Marshall acknowledges that this is less convincing for some because it is rather subjective, but evangelicals will likely agree with the overall concept.
Finally, I think it is helpful to recognize that holding the NT documents as the primary sources does not mean to suggest that we shouldn’t consult secondary works. As Michael F. Bird has stated in his recent JETS article (see my review here), those sources can really help our understanding of the biblical text. Marshall wisely writes,
“To adopt this procedure, of course, does not lead to excluding other works outside the New Testament from consideration. In elucidating the content of the New Testament and in reconstructing the history of the period it is essential to make use of all other relevant sources, including other early Christian literature… If we are writing an account of the theology of the New Testament, then our task is to expound its content, just as the exposition of the thought of Shakespeare will draw upon his writings but will do so in the context of the works of other Elizabethan playwrights…” (p. 29)
So what’s the point? When you want to know what the NT says on a certain subject, you have good reason to begin by reading the NT!