Since you have admitted that the Gentiles are without "the law" in verse 14 then the Gentiles must be those people in verse 12 who have sinned "WITHOUT the law" whereas it is the Jews in verse 12 that have sinned "in the law" as verse 10 restricts all who come into judgement as either Jews or gentiles. Hence, since those who "have not" the Jewish law are Gentiles then they must be those in verse 12 who have SINNED "without THE LAW" and those in verse 12 who have sinned "IN the law" must be Jews and on judgement day the Jews will be judged by the JEWISH LAW.
Hence, TWO laws just as you say, one for the Gentile, another for the Jew in the day of judgement both of which have been "SINNED" against and thus the law the Gentile sinned against they will "PERISH" by just as the law the Jews have sinned against they will be judged by.
Hence, your following comment is wrong as the Gentiles do not obey it but already in verse 12 have been condemned by it as those "SINNED" and therefore will "PERISH" by it.
Verse 12 already identifies both the Gentiles and the law they have "SINNED" and it is not the Jewish law. Hence, this flatly denies your contention they have obeyed it. Verses 14-15 simply identify and define what law it is that is not Jewish which they have "sinned" against and in the day of judgement will be used to judge them so they "PERISH" by it.
Verse 13 refers to "the law" that can be HEARD and since there are only TWO options in verse 12 then it can only refer to the JEWISH LAW. The gentiles are "WITHOUT" the Jewish law but have nevertheless "sinned" against and will "perish" by the law they have sinned against. God never gave the Gentiles a law that can be HEARD! That leaves only the Jewish law as it is the only other law in verse 12. The Jewish law was read regularly every Sabbath day and was HEARD by all the Jews.
I have pointed out TWO laws for TWO kinds of people beginning in verse 10-12. The context is the day of judgement and there are only TWO types of people present - JEWS and GENTILES (v. 10) but God will not respect their persons whether Jew or Gentile (v. 11). The Gentile was not given the Jewish law (v. 14) so is the one who has SINNED "without THE LAW" and will "PERISH without the law" of Moses, whereas the Jew was given the Law and is therefore those who have SINNED "in the law" and will be judged by the law" of Moses. The Gentile never obeyed the law they were under as Paul says clearly they have "SINNED" in it. The Gentiles never obeyed the law they were under any more than the Jew has obeyed the law they have "SINNED" in. The gentile will "PERISH" under the law they have "SINNED" just as the Jew will be judged and perish under the law they have "SINNED" in.
So far in this context the law that the Gentile has "SINNED" against and will "PERISH" under in verse 12 has not been identified by Paul except by contrast - it is "WITHOUT the law" of Moses.
Verses14-15 identifies and defines what law the Gentiles have "SINNED" against and will "PERISH" by, that is not the Law given to the Jews (v. 14a). It is the law that is given them in regard to their "nature" by physical birth - the conscience. The term "nature" is used immediately before this text and after it and it means that which is in keeping with God's design for human nature.
For example, it is used to show that homosexuality is contrary to God's design for human nature in Romans 1:26-27.
For example, it is used in Romans 2:27 to show that circumcision is not natural by birth but occurs in response to the letter of the law.
Likewise, Paul defines the law that Gentiles have sinned against in verse 12 and which they will "perish" by in the day of Judgement to be what God has given them in His design of human nature - the conscience.
14 For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves:
15 Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another
If Paul is not defining in verses14-15 what the Gentile has sinned against and will perish by in verse 12 then there is no contextual identity of the law they have violated in verse 12.
There is no reasonable or rational way that Romans 2:14-15 is talking about any kind of Christians whether Jew or Gentile. He has already claimed the Gentile has broken this law in verse 12 and there are only two options given in verse 12 not three!
There is no way the term "nature" in verse 14 can refer to the new birth as the term is consistently used before and after verse 14 by Paul to mean those things associated with or contrary to the PHYSICAL BIRTH or the ordinary (Rom. 1:26; 2:27). Even in Romans 11:24 it means the ordinary. Grafting branches of a tree into another tree is not ordinary or keeping with how it naturally grows.
Paul is defining the law that the Gentiles have SINNED against in verse 12 and by which they will "PERISH" by as conscience will be used on the day of judgement as a WITNESS against them:
15
Which shew the work of the law written in their hearts, COLOR="DarkRed"]
their conscience also bearing witness,
and their thoughts the mean while accusing or else excusing one another.
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In the day when God shall judge the secrets of men by Jesus Christ according to my gospel.