As for their anxious scruples about foods, their superstition concerning the Sabbaths, their boasting about circumcision, and their pretense regarding fasting and new moons—things that are laughable and not worth discussing—I do not think you need to learn about them from me.
For among the things created by God for human use, to accept some as well created but reject others as useless and superfluous—how is that not impious?
And to speak falsely about God as though he forbade doing anything good on the Sabbath day—how is that not impious?
And to boast that the cutting of the flesh is a sign of election, as though for this reason they were especially loved by God—how is that not worthy of ridicule?
And to keep watch on the stars and the moon in order to observe months and days, dividing God's ordering and the changes of the seasons according to their own impulses, some into festivals and others into times of mourning—who would regard this as a sign of piety rather than, much more, of folly?
I think you have been sufficiently instructed as to why Christians rightly keep away from this common vanity and deception, and from the Jews' excessive observance and boasting. But as for the mystery of the Christians' own religion, do not expect to be able to learn it from a human being.