Ethics deals with the moral principles that guide our thoughts and actions. Christian ethics is based in what we find in the New Testament. Expressing a biblical system of ethics is an important part of sharing the gospel.
Philosophical naturalists believe that the physical universe is all that exists. As a result, they reject the idea of God, and the idea that morality - our sense of right and wrong, and what ought to be - comes from God. Can morality be explained in purely physical terms?