in that they show the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them,Romans 2:15(NASB)
In the earlier verses of Romans chapter 2, Paul explained that although the Law of Moses was not given to Gentiles, nevertheless they have been endowed with an innate knowledge of what is good and evil. Because man was made in the image and likeness of God they have a God-given conscience by which they instinctively know what is right and what is wrong.. what is good and what is evil - what is moral and what is immoral. Although Gentiles do not have the law... they actually become a law unto themselves, because moral laws are effectively written within their conscience - they are written in their heart.
Although the Mosaic Law was given to Israel alone, gentile nations do have a God-given in-built code of conduct which reflects God's moral laws and requirements. The inner conscience of man shows that the work of the Law is written deep within the heart of every-man. It means that their outward behaviour is an indicator of whether or not they listen to their own, inward conscience and respond appropriately - or whether they ignore the inner sense of right or wrong and disregard the promptings of the heart.
It is not the actual Mosaic Law which is written within the heart of Gentiles. It is rather an inner law that is written within the heart of every-man - a witness that guides Gentiles to know what is right and to know what is wrong.. for we read that when Gentiles who don't have the Law do instinctively the things that the the Law command - they demonstrate that they are a law to themselves - by following their conscience - for good or for evil.
Sone do what is good because they heed the call of their conscience while other do what is wrong by ignoring this inner, moral witness - but whether they heed the promptings of their conscience to do what is right OR go against the persuasion of their conscience and do what is wrong - they are taking heed to a God-given moral code, such that their actions either approve their right choice or condemn their wrong choice. But either way it is their conscience; which influences their actions and the choices they make, which either defends or accuses them... Paul explains it like this: they show the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them.
Heavenly Father, I confess that in and of myself there is no good things and that there is nothing that commends me.. but thanks be to God that by faith in Jesus Christ my sins have been forgiven, I have received eternal life and I am accepted as Your child because of His righteousness - praise His holy name, AMEN.