Many authors of Paul’s day referred to the “unwritten law” within man. They thought of it as something that pointed man to the right way. Though it is not embodied in written laws, it is in some ways more important than the written law. We have to be obedient to conscience, the work of the law residing in ourselves.
Though God has His work within every man (resulting in conscience), man can corrupt that work, so that conscience varies from person to person. We also know that our conscience can become damaged through sin and rebellion, but then can be restored in Jesus.
If our conscience is condemning us wrongly, we can take comfort in the idea that God is greater than our heart (1 John 3:20).
On the day when God will judge no man will escape God’s judgment by claiming ignorance of His written revelation. Violating God’s internal revelation is enough to condemn us all. God does not Show Favouritism.