Romans 2:12-16

¹² “For all who have sinned without the law will also perish without the law, and all who have sinned under the law will be judged by the law; ¹³ for it is not the hearers of the law who are righteous before God, but the doers of the law who will be justified. ¹⁴ 

For when Gentiles who do not have the law instinctively perform the requirements of the law, these, though not having the law, are a law to themselves, ¹⁵ in that they show the work of the law written in their hearts, their conscience testifying and their thoughts alternately accusing or else defending them, ¹⁶ on the day when, according to my gospel, God will judge the secrets of mankind through Christ Jesus.”

This language would have been especially difficult for the Jews to receive. Paul is taking away their pride in having the law by showing that it’s not about having the law per se. It is about performing according to its standards.  Gentiles have a knowledge of the truth, a conscience.  So, even if the Gentile doesn’t have the law, but instinctively behaves according to the standard of the law, God would count this as righteousness.