That scripture is proof it is about the ceremonial works.
Romans 9:30 What shall we say then? That the Gentiles, which followed not after righteousness, have attained to righteousness, even the righteousness which is of faith.
Look how many times Paul speaks of the ceremonial work CIRCUMCISION, in Romans alone.
Romans 2:25Circumcision has value if you observe the law, but if you break the law, you have become as though you had not been
circumcised.
Romans 2:27 The one who is not
circumcised physically and yet obeys the law will condemn you who, even though you have the written code and
circumcision, are a lawbreaker.
Romans 2:28 A person is not a Jew who is one only outwardly, nor is
circumcision merely outward and physical.
Romans 2:29 No, a person is a Jew who is one inwardly; and
circumcision is circumcision of the heart, by the Spirit, not by the written code. Such a person’s praise is not from other people, but from God.
Romans 3:1 [ God’s Faithfulness ] What advantage, then, is there in being a Jew, or what value is there in
circumcision?
Romans 4:11 And he received
circumcision as a sign, a seal of the righteousness that he had by faith while he was still uncircumcised. So then, he is the father of all who believe but have not been circumcised, in order that righteousness might be credited to them.
Nowhere anywhere does Paul say not of obeying. He is saying not of circumcision.