New Testament writers often cite or allude to the Old Testament to make theological points. In this way, the Old Testament forms the narrative sub-structure behind the New Testament, always present but not always explicitly so.
Through careful study, students of the Bible can discover citations, allusions, and echoes of the Old Testament throughout the New Testament. For example, Romans consistently quotes the Old Testament to argue theologically. Consider, for example, how Paul cites Abraham’s experience in Genesis 15 to substantiate the doctrine of Justification in Romans 4.
With that said, a person could easily spot a problem here. If it takes diligent study to discern what Paul quotes and how he interprets the Old Testament, can we actually assume that Paul’s audience in Rome really knew the Old Testament well enough to pick up Paul’s argument? What about gentile audiences who didn’t know the Old Testament very well? Could they have picked up on Paul’s subtle uses of the Old Testament?
I think the answer would have to be, no; they didn’t always pick up on what Paul said or did. But this is not a serious problem. After all, Paul’s whole way of thinking was heavily invested in the Old Testament, and he rarely cited an Old Testament text without explaining what it meant. Stanley Porter makes these two points, rightly I think, in his recent work on the New Testament’s use of the Old Testament:
As interpreters, we have probably placed too much emphasis on trying to understand Paul’s citations from the standpoint of his audience, rather than closely examining how Paul is thinking through Scripture and using it to develop his argument. (Porter, 2016: 28)
Paul rarely depends simply upon citation of an OT quotation without exposition to substantiate a point in his theological argument. (Porter, 2016: 28)
The fact is we will never know what Paul’s audience really knew or didn’t know. But we do know that Paul was a pharasaic Jew whose world revolved around the Old Testament (cf. Porter, 2016: 28). We could thus expect him to think and argue in Biblical ways to verify his theological assertions. Yes, his audience may not have picked up on all of the depth of Paul, but they surely understood his main point.
Don’t preachers do this today? They sit in their studies, combing over the Biblical text before preaching the main point on Sunday. Their congregation could not be expected to know all the details of the passage at hand, but they know the main ideas. And, if the pastor did a good job, they can pursue study of the Scripture like the Bereans did. In fact, Paul’s audience could too, since they would have had his letters to memorize and ponder over for years.