“Paul assesses the significance of Israel and the Sinai covenant within the larger biblical narrative. It is this essentially salvation-historical reading of Genesis that enables him to come within a whisker of treating the Sinai covenant as a parenthesis: the law’s most important function is to bring Israel, across time, to Christ—and to bring others, too, insofar as the ‘law’ is found among those ‘without the law.’
Here, then, too, we obtain a glimpse of how something could be simultaneously long hidden / eventually revealed and long prophesied / eventually fulfilled. It was right there in the text (provided one reads the Scriptures with careful respect for the significance of the historical sequence), even though, transparently, this was not how it was read by Paul the Pharisee.
Doubtless it took the Damascus road Christophany to make Saul of Tarsus recognize that his estimate of Jesus was wrong: Jesus could not be written off as a (literally) God-damned malefactor if in fact His glorious resurrection proved He was vindicated, and so the controlling paradigm of his reading of the Old Testament had to change.
But when it changed, Paul wanted his hearers and readers to understand that the Old Testament, rightly read in its salvation-historical structure, led to Christ.
In other words, as far as Paul was concerned the gospel he preached was announced in advance in the Scriptures, and was fulfilled in the events surrounding the coming, ministry, death, resurrection, and ascension of Jesus—even if this gospel had long been hidden, and was now revealed in those events and thus in the gospel Paul preached—the gospel revealed, indeed, through the prophetic writings.”
–D.A. Carson, “Mystery and Fulfillment: Toward a More Comprehensive Paradigm of Paul’s Understanding of the Old and the New,” in Justification and Variegated Nomism: The Paradoxes of Paul (ed. Peter T. O’Brien and Mark A. Seifrid; vol. 2, 181st ed.; Wissenschaftliche Untersuchungen zum Neuen Testament; Grand Rapids, MI; Tübingen: Baker Academic; Mohr Siebeck, 2004), 2: 427–428.