It is not the hearers of the law who are righteous before God; it is the doers of the law who will be justified.
In context
11God shows no favoritism. 12All who sinned without the law will also perish without the law, and all who sinned under the law will be judged by the law. 13It is not the hearers of the law who are righteous before God; it is the doers of the law who will be justified. 14When Gentiles, who have no law, do by instinct what the law requires, they are a law to themselves, though the law is not theirs. 15They show that the work of the law is written on their hearts, their conscience bearing witness alongside, their thoughts accusing them or even speaking in their defense