"And their eyes were opened, and they knew him; and he vanished out of their sight. And they said one to another, Did not our heart burn within us, while he talked with us by the way, and while he opened to us the scriptures?" Luke 24:31-32
The questions surrounding the unity of the canon can be explored a little further by examining one subset of this topic, viz. the use of the OT in the New. During the last four decades, a vast quantity of work has been done in this area. Here we may merely identify three aspects of this work that have a bearing on biblical theology, without probing any of them very deeply.
1. One of the most intriguing aspects of this subject is the warrant provided, if any, by the NT writers, when they draw theological conclusions from the OT. While many scholars have shown that the NT writers' appropriation techniques find parallels in the Jewish writers of the second temple period when they use the Hebrew canon, such observations do not adequately account for the different conclusions reached by Christian Jews like Paul and by non-Christian Jews. Some scholars (e.g. D. J. Moo) have advanced the debate by distinguishing between appropriation techniques and hermeneutical axioms; the former may be shared by Christians who wrote the NT and by Jews, but disjunctions surface when the latter are studied closely. For instance, many conservative Jews saw in the law given at Sinai not only a body of instruction but a hermeneutical key to the rest of Scripture. In contrast, some NT writers insist that the proper place of the law-covenant can be grasped only when it is properly located in the stream of redemptive history (hence Paul's argument in Gal. 3, or the argument of Heb. 7). It follows that the kind of biblical theology that is profoundly grounded in tracing out the Bible's plot-line is intrinsically more likely to pick up this kind of inner-canonical hermeneutical distinctive than either systematic theology or those kinds of biblical theology that rarely ask diachronic questions.
2. More challenging, certainly more technical, are the countless quotations from, allusions to, and echoes of the OT found in the NT. Many, of course, are straightforward. But many raise fundamental questions. Psalm 2:7 is quoted three times in the NT , once to justify the claim that Jesus has been raised ( Acts 13:32-33 ), once to prove that Jesus is superior to angels ( Heb. 1:5 ), and once to demonstrate that Jesus did not take on himself the authority of high priest, but was appointed to the task by his Father ( Heb. 5:5 ). At the surface level, Psalm 2:7 warrants none of these conclusions. Indeed, the disparity prompts many scholars to conclude that the NT writers frequently use the OT in an irresponsible proof-texting way that badly rips texts out of their contexts (e.g. B. Lindars). Others reverently appeal to the revelatory stance of the NT authors, who thus found more in the OT text than was actually there on the surface. The NT writers thus deployed an approach to textual citation that cannot be duplicated today by readers of the OT (e.g. R. Longenecker). Still others hold that close scrutiny of these challenging passages discloses some profound assumptions, themselves grounded elsewhere in exegesis, regarding interlocking typologies having to do with David, the temple, the priesthood, and other subjects. If these latter approaches are valid, they have an enormous bearing on how one should properly read the Bible. Moreover, they are the very stuff of biblical theology that seeks to track the Bible's storyline and explore the significance of the canon.
3. During the last two decades many have come to speak of ‘intertextuality' in preference to ‘the use of the Old Testament in the New'. In some usages, the two expressions are roughly synonymous. More commonly, however, intertextuality refers to a broader phenomenon, not only because it includes in its purview the use of earlier texts by later texts within each Testament, but also because it explores how the later texts, duly absorbed by the contemporary interpreter, cast a shadow back on the meaning the interpreter finds in the earlier text. Among some exponents of intertextuality, this generates blatant anachronisms. Such anachronisms are inoffensive, however, to those with the strong postmodern conviction that meaning rests primarily with the interpreter and not with either the author or the text. Among more cautious exponents of intertextuality, anachronism is carefully avoided, while the interpreter seeks to identify textually based markers that attest an earlier passage as truly an adumbration of something that will develop only later, an anticipation of something still obscure, the beginnings of a typology that develops across the sweep of redemptive history. Carefully exploited, intertextuality proves to be one of the lashings that hold biblical theology together.