The Midrash Mash
In its softest form, it might simply mean that Paul is commenting on Scripture in such a way as to apply it to his own time and place. This, while true, is also trivial: “in that sense, all readings of Scripture by Jews and Christians always and everywhere are instances of midrash.”
A stronger claim is that the type of midrash practised by the rabbis is the best historical background against which we can understand what Paul is doing in his letters. Formal similarities may be identified (although these usually crumble under close inspection); there may be a similarity of hermeneutical method, perhaps utilising the same methods as the rabbis did (although only two of these appear with any frequency in Paul).
Often, however, the term is used with such vagueness that it mainly serves “as a convenient cover for a multitude of exegetical sins.” To say that Paul is engaging in midrash, in such contexts, is apparently a way of getting him off the hook for reading the Old Testament in a bizarre way: “One frequently finds Christian commentators explaining away their embarrassment over some piece of fanciful Pauline exegesis by noting solemnly that this is midrash, as though the wholesome Hebrew label could render Paul’s arbitrariness kosher.” Or, even worse, midrash is used as shorthand for “free and playful interpretation,” with no real connection to any known practice of biblical interpretation.
The problem throughout, Hays argues, is that “the label midrash tends to bring the interpretive process to a halt, as though it had explained something, when in fact we should keep pressing for clarity.” This doesn’t mean it should never be used, but it does mean that it should provide the starting point for investigation, rather than the finishing point.