The primary distinction between Christian and secular ethics is that the first are derived from Christian teachings, whereas the second are not. Instead, secular ethics claim a mooring in attitudes not beholden to religion of any kind, but to a shared sense of humanity. This is not to say, however, that certain values or ethics might not be held by both.
For much of Western history since the conversion of Rome, ethics have been highly influenced by Christian precepts. These include not only the teachings of Jesus, but also Old Testament law as well. Regardless of denomination, Christian ethics affected nearly every aspect of society and shaped the way most people thought about right and wrong.
Beginning with the Enlightenment, Christianity became increasingly challenged as the sole source of intellectual and moral authority, and new secular attitudes took hold. In the succeeding centuries, a movement commonly called secular humanism gained considerable traction and challenged any claim of religion to govern ethics unilaterally. Taking human beings to be the single most important site of value, a secular ethics emerged which argued that if humanity was properly oriented toward establishing its own worth, then religion would become largely, if not entirely, unnecessary.
According to the American Humanist Association, it is important to point out that religious and secular ethics, while divergent in source, can be exactly the same in terms of what they value. The sanctity of human life; the development of a compassionate society; the furtherance of learning: all of these things and more can be embraced by both Christian and secular moralists. The important difference is in deciding where those ethics derive their authority, from God or from human beings.