I mentioned here what I think is an implausible way to relate grace and conditions or the lack thereof. It occurred to me that getting back to the Reformation earlier than the Westminster Standards might be helpful:
And indeed one may easily get in trouble here unless one proceeds on the royal highway. For those people who consider only the conditions of the covenant and in fact disregard the grace and promise of God exclude infants from the covenant. It is true that children not only do not observe the terms of the covenant but also do not even understand these terms. But those who view only the sacrament, ceremony, or sign of the covenant count some in the covenant who are really excluded. But if you consider each one separately, one at a time, not only according to the conditions of the covenant but also in terms of the promise or the mercy of God, and the age and reason of a person, then you will realize that all those who believe from among the Jews and the Gentiles are the descendants of Abraham with whom the Lord made the covenant. In the meantime, however, their offspring, that is, their children, have by no means been excluded from the covenant. They are excluded, however, if having reached the age of reason they neglect the conditions of the covenant.
In the same way, we consider children of parents to be children and indeed heirs even though they, in their early years, do not know that they are either children or heirs of their parents. They are, however, disowned if, after they have reached the age of reason, they neglect the commands of their parents. In that case, the parent no longer calls them children and heirs but worthless profligates. They are mistaken who boast about their prerogatives as sons of the family by virtue of birth. For he who violates the laws of piety toward parents is no different from a slave; indeed, he is lower than a slave, because even by the law of nature itself he owes more to his parents. Truly this debate about the seed of Abraham has been settled for us by the prophets and the apostles, specifically that not everyone who is born of Abraham is the seed of Abraham, but only he who is a son of the promise, that is, who is faithful, whether Jew or Gentile. For the Jews have already neglected the basic conditions of the covenant, while at the same time they glorified themselves as the people of God, relying on circumcision and the fact that they were born from the parent Abraham. Indeed, this error is denied and attacked not only by Christ along with the apostles but also by the entire body of the prophets (boldface added).
Thus wrote Heinrich Bullinger in The One and Eternal Testament or Covenant with God, which I found translated in Fountainhead of Federalism: Heinrich Bullinger and the Covenantal Tradition, Charles S. McCoy and J. Wayne Baker [Louisville, KY: W/JKP, 1991], 106). Notice that Bullinger doesn’t say that Jews are guilty in boasting in their obedience to the Law, but only in their membership in the Abrahamic family through circumcision. In my opinion, pursuing this as you study Romans would be very helpful to understanding what Paul is saying.