Locke is looking for a new way to understand how moral choices are made. He talks about natural law, which is like a set of rules that come from a higher power. Locke says that only beings who can understand these rules and have a reason to follow them should be held accountable. He believes that we can figure out these rules using our brains, and we follow them because it makes sense to us. Our duty to follow these rules comes from a deep sense of obligation.