According to Christians, everyone of us knows the right way to behave because God has written his laws in our ‘hearts’. We don’t always bother to consult what he’s written there, however, because we prefer to do our own thing, which is when our consciences start to bother us about our wicked ways. Here’s how Paul put in Romans 2.15:
Gentiles 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.
There’s no evidence that this is how it works, of course; Paul never cared much for evidence nor even for making sense. We know that, provided we are not born with psychopathic tendencies, we learn values, morals and how to relate to others from care-givers in our early lives. They teach us to share (or not) and how we should treat other people, and while it’s true we do seem to be born with a sense of empathy – watch a young child respond to the distress of another – this needs to be cultivated and nurtured. A knowledge of the 613, frequently absurd stipulations of the Old Covenant (which is what Paul is referring to) is demonstrably not genetic; we do not have an innate or instinctive understanding of God’s requirements. Psychologists point to the fact that it is only when she is three that a child learns that stealing is wrong; she is not born knowing it.
All of which is a far cry from ‘God’s law being written in (our) hearts’. Even if Paul meant we have a sort of general, non-specific understanding of how we ought to behave – though this is not what he actually says – there is no evidence this has been planted in us by a supernatural being. Certainly not one that thinks slavery is okay and whose prohibition against killing doesn’t extend to tribes beyond one’s own.
The Christian approach to morality puts me in mind of Charlotte’s Web. In that great children’s book, Charlotte the spider adds messages to the webs she spins to help save her friend, Wilbur the pig, from slaughter. When the gullible humans in the story see ‘Some Pig’, ‘Radiant’, ‘Amazing’ and ‘Humble’ written in the webs, they inexplicably give the credit, not to Charlotte, but to Wilbur. No-one, either in the book itself nor in reviews, comments on the fact that it is not Wilbur who has these qualities, despite what the messages say, but the creature who made them (an anomaly I’m sure E. B. White was aware of when he wrote the book.)
If I might interpret Charlotte’s Web allegorically, we humans are Charlotte, while Wilbur, on whom everyone seems focused, is God. It is we who have developed moral codes throughout our existence, the latest versions of which our children learn from us, and attempt to follow (or not). Meanwhile, the likes of Paul and contemporary Christians refuse to give us one iota of credit. Instead, they insist, the credit goes to their god; a being nowhere near as pleasant as Wilbur, though he’s every bit as fictional – another of our creations, just like those moral codes we invented.