Everything is subjective

The entire reason that natural law exists is because of the ambiguity surrounding the concept of "good." Killing or stealing is not good, we all know that. But wait- says who? God? Government? We don't really know why some things are good, so we construct basic moral tenets in order to guarantee some semblance of equality and assurance to everyone. Why can't you kill or steal? Because it adversely affects other people. Natural law says that you can basically do anything you want as long as nobody gets hurt from you doing it. Law was devised to ensure equality for all, and human beings, born and bred with a conscience, instinctively know this. Before being told about natural law, most people have a basic understanding of it, even if they don't know that it's called natural law. Once we gave a name to the concept, it was more easily recognizable. It was based on being good, and then the question of "what is 'good?'" came up. That's why we invented God-- so we could have some absolution when it came to the question of good and evil. So there you have it: Human beings innately understand the concept of natural law, which raises the question of the definition of goodness, which is why God was created.