God as potter, humans as clay: various Old Testament texts use the image (e.g., Isa 29:15-16; 45:9-11; 64:8-9; Jer 18:1-12). If the issue here is God’s right to incorporate the gentiles as gentiles into God’s people, the most relevant parallel is Isa 45:9-11, which looks like a response to questions about God’s right to name the pagan Cyrus “the anointed” (Messiah!) to redeem Israel.
Works vs. faith in vv.31-32a: it’s probably too simple to interpret this simply as competing strategies for Torah implementation: implementation for the purpose of excluding vs including the Gentiles. But Torah (or Gospel) as instrument of exclusion or inclusion is not irrelevant either.
Verses 32b-33 merge Isa 8:14 and 28:16. There’s evidence that some of Paul’s contemporaries were reading both texts as messianic, so it would make historic sense to read the stone as Jesus. So we might wonder: what relation—if any—is there between Paul’s faith/works contrast and the issues the Gospels portray as separating Jesus and his religious opponents? (More on this tomorrow.)
Postscript: I have been looking for a reading of Paul that renders his various statements about the law consistent. The challenges of that search have me currently reading E. P. Sanders’ Paul, the Law, and the Jewish People, who argues that Paul’s consistency consists in a number of central convictions, e.g., “that God had sent Jesus Christ to provide for the salvation of all; that salvation is thus available for all, whether Jew or Greek, on the same basis,” that God does things for good reasons, and works back from these to offer different (inconsistent) answers to questions like what is the law for, in what does Israel’s failure consist. Clearly a perspective worth considering.