Scott Rae, in the introduction to his book Moral Choices: An Introduction to Ethics, lays out some of the reasons the study of ethics is important and why the modern assumption of naturalism endangers the concept of even a good life:
Most people, when they are genuinely being honest with themselves, associate doing well in life with being a good person. Having moral character is still essential to most people's conceptions of what makes a person flourish in his or her life. For example, it is difficult to imagine a person being considered a success in life if he has gained his wealth dishonestly. It is equally difficult to call a person a success who is at the top of his profession but cheats on his wife, abuses his children, and drinks too much. On the other hand, we rightly hold up a person like Mother Teresa as a model of living a good life, even though she lacked most material goods that society values. One of the principal reasons for being moral is that it is central to most concepts of human fulfillment. For the Christian, being moral is critical to a life that seeks to honor God. We could say that being moral is inherently good because it is foundational to a person's flourishing in life, since doing well in life and being a good person still go together for most people.
These reasons for the importance of studying ethics all presume that there is as genuine moral knowledge. But that notion is being increasingly called into question in philosophy today as a result of the cultural dominance of the worldview of naturalism. Among other things, the naturalist holds that all reality is reducible to that which can be perceived with one's senses—that is, there is nothing that is real or counts for knowledge that is not verifiable by the senses. As a result, moral knowledge has been reduced to the realm of belief and is considered parallel to religious beliefs, which the culture widely holds are not verifiable. The theist maintains that moral knowledge is genuine knowledge in the same way that scientific knowledge is real—that the notion that "murder is wrong" can be known .as true and cannot be reduced to subjective opinion or belief without the risk of all morality being subjective. The theist argues that no one lives consistently, as though morality were entirely subjective, and that moral truths do exist and can be known as such.1