By Nature

Romans 2:14-16 ESV

14 For when Gentiles, who do not have the law, by nature do what the law requires, they are a law to themselves, even though they do not have the law. 15 They show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them 16 on that day when, according to my gospel, God judges the secrets of men by Christ Jesus.

The use of the word nature in verse 14 is explained in verse 15. It is not by nature that we have the law, for it has to be written on our hearts. Our nature comes into play through our conscience. Conscience is part of the "image of God" in which we are made. Conflict arises in the difference between our spirit and the Holy Spirit. The secrets of the heart are exposed in this interplay. It is here that God works, as mysteriously as a seed grows once planted in the soil.