Here are some thoughts I have regarding the Gentiles who do instinctively the things of the law.
From Jack Crabtree’s translation of Romans, Portion One/Section 1/Part 5/paragraph #14:
3) It is not the hearers of the divine commandments who are dikaios before God; rather, it is the doers of the divine commandments who will be deemed dikaios. 4) Indeed, when Gentiles, who do not have the Covenant by natural birthright, do the things required by that Covenant—even though these people do not possess the Covenant for themselves—such things are a covenant. 5) Such people demonstrate the deed required by that covenant written on their hearts[.] (See Romans 2:13-15 in your “real” Bible.)
These real (or hypothetical) Gentiles are not “God fearers” in the sense that they are merely not familiar with the Judaic law or the particulars of the various covenants. These are true pagans or non-religious individuals who know absolutely nothing of the God of Abraham and Moses. When they “do the things required by that covenant” this is not that they have figured out somehow (intuitively?) what the covenant is and then began keeping a list of commandments. From the outside there may be nothing about these Gentiles that would make them appear as devout Jews.* What this implies is that the hearts of these Gentiles have come to a place whereby (one could imagine) they might stumble upon the Sermon on the Mount, for example, and say, “Yes! That’s true. I long for that.” It follows, then, that when Paul here is arguing to “do the things required by that Covenant” he is thinking not of dietary laws or keeping the Sabbath. Neither is he thinking of a personal relationship with Jesus Christ. I imagine Paul has in mind the list we call the beatitudes – being poor in spirit, being a peacemaker, being someone who thirsts after righteousness, etc. To be poor in spirit, to be a peacemaker, to thirst after righteousness, is to do the things required by the covenant.
What does this mean for us? I think we need to constantly examine our tendencies to create lists of particulars by which we judge others and ourselves. Just like the Jews of Jesus’ day, we too have our rules, our mental covenants that we live by. We judge our spirituality, our faith, our righteousness by these lists, and each of us always come out better in our own minds than do anyone else to whom we apply the standard. But we know this, we hear this on Sunday. The frightening reality is that deep down we know that to truly live as the beatitudes call us would produce people who might not look much like us or the other Christians around us. What is more frightening, we cannot become the people who live the beatitudes by choice. The beatitudes are thrust upon people, mark people, at times against their will.
* I think we have to assume, as well, that there may be nothing about these Gentiles that would make them appear as “devout Christians” either.