This became a rather common accusation of the Church Fathers against the Jews - namely, that before Jesus came, the Jews had obstinately refused to observe the (Old) Law that was then binding on them; but now that this Old Law has been superseded by a new Law, they obstinately insist on observing it piously!
Question: How is this effective as a polemical "answer" to an important question that might have been raised about the practicing Jews of Chrysostom's time?