First, because it shows us that sin is very bad but grace is better. Because of sin, everybody after Adam and Eve is born imperfect. We’re instinctively broken and depraved rebels against God (Rom. 3:9–12). It sounds harsh, but it’s true. Nobody’s born loving God. Instead, our natural inclination is to hate him. The gospel is only good news because there’s bad news. That terrible news is that sin is real, and we are sinners. The punishment for our sin is death (Rom. 6:23). We rebelled against an