There is only one and the same Gospel for Gentiles and Jews . . . There is no partiality; but the Word and its teaching are one and the same for all men, no matter how diverse the mask or social position may be. The apostles circumcised; Paul did not. But both he and the apostles left circumcision free for those who had been born in it, for the apostles could distinguish the Gospel from the law in a way that was both wise can correct. I also believe that if the believing Jews at the time had observed the law and circumcision under the condition permitted by the apostles, Judaism would have remained standing until now, and the whole world would have accepted the ceremonies of the Jews. But because they insisted on the Law and circumcision as something necessary for salvation and constructed an act of worship and some sort of god out of it, God could not stand for it (“Lectures 1535”, Luther’s Works, vol. 26, 104-05).
I find the comment about the whole world accepting the ceremonies of the Jews filled with irony. Luther however seems to follow Augustine’s view that the early Jewish believers continued to follow the Mosaic Torah, perhaps excluding Paul.