Gentiles, who do not have the law, do by nature what the law requires: This fits with the idea that the law is written on their hearts (2:15), which points to the promise of the new covenant (Jeremiah 31:31–34).
Or Paul may be speaking about non-Christian Gentiles. These Gentiles know God’s basic moral law through their conscience. In this case, Paul shows that all people can be held responsible for basic moral standards, even without God’s written law.