Christian writers discerned harmony between Greco-Roman invocations of natural law and St. Paul’s observation that the Gentiles were instructed by ‘the law written in their hearts’ (Rom. 2:15). St. Paul observed that even pagans have some knowledge of God [ … ] Yet when pagans failed to give thanks to God, they fell into idolatry and other vices, including unnatural sexual relations (1:26-7). Yet at times, Paul observed, pagans have done ‘by nature’ deeds required by the Law even without the benefit of positive biblical revelation. Thus all people will justly receive divine judgement: Jews according to their own observance of the Law of Moses, pagans in terms of their observance of the ‘law written on their hearts’ (2:15).
St. Paul was later taken to support Christian adoption of natural law by Patristic authors in the early centuries of the church. St. John Chrysostom (d. 407), for example, believed that every person has access to natural law in his or her natural reason: ‘In creating man at the beginning, God placed within him a natural law.’ The law of nature exists prior to civil statutes and is their judge. The Fathers also believed natural law was indicated in various scriptural texts, including denunciations of the violation of basic moral awareness by the ‘nations’ (Amos 1), appreciation of the ordering of creation (Ecclesiasticus 39:21), and appeal to God’s original intention in creation (Matt. 19:3-8).
Stephen J. Pope, Natural Law and Christian Ethics in The Cambridge Companion to Christian Ethics, ed. Robin Gill (Cambridge University Press: 2001) pp. 77-78