Everyone has a set of standards that they follow to determine right from wrong, and these standards and the process by which they are formulated consist of a system of ethics. Religion is a powerful determining force for ethical behavior, and the vast majority of people worldwide base their ethical decisions on the particular religion that they follow. Christianity is currently the religion with the most adherents worldwide, so Christian ethics help billions of people determine right from wrong each day.
Christian Ethics: A Definition
Ethics determine what is right and wrong, and from a Christian perspective, proper ethical theory is grounded in what is pleasing to God. Professor John Frame provides a good definition of ethics on page 10 of his book The Doctrine of the Christian Life. In his view, ethics is "a means of determining which persons, acts, and attitudes receive God's blessing and which do not." That which is right receives God's blessing, and that which is wrong does not enjoy his favor. This basic definition is an excellent overview of what ethics means to the Christian, and virtually every Christian tradition relies on natural law, Scripture, and church tradition as authorities for an ethical system. Yet the authority that tends to receive the most emphasis in formulating ethics varies in the three main traditions of Christianity: Roman Catholicism, Eastern Orthodoxy, and Protestantism.
Roman Catholic Ethics
Operating under the strong influence of Saint Thomas Aquinas, who accentuated mankind's ability to learn about God from nature, Roman Catholic ethicists tend to stress natural law in their formulation of a Christian ethical theory. Natural law looks to nature and tries to figure out the purpose for which things exist, the reason why certain things are what they are, and so on. Standards of right and wrong are based on the right use of the things in nature. For example, Roman Catholic ethics will argue strongly for a pro-life position because nature shows us God made all human beings to live and not die, and therefore it is unjust to take the life of another human being except in extraordinary circumstances. Roman Catholicism will rely on Scripture and tradition as well to formulate ethics, but natural law is definitely an emphasis in their formulation of ethical standards.
Eastern Orthodox Ethics
Eastern Orthodox ethics such as would be taught at an Eastern Orthodox seminary pays close attention to church tradition as a standard for ethics. Particularly important are the church fathers and the formulations of the first seven ecumenical councils. In the Orthodox view, something is right if the early tradition, reflecting the presence of the Holy Spirit in the church, defines it as right and proper. An ethics essay that would argue for the pro-life position in Eastern Orthodoxy would emphasize the pronouncements of the early councils in defining what receives God's blessing. Eastern Orthodox ethicists will also lean on Scripture and natural law, but church tradition is the key authority in their ethical systems.
Whether the subject is corporate ethics, reproductive ethics, political ethics, and so on, Christian ethicists in the Protestant tradition rely chiefly upon the Bible in putting together an ethical theory. Tradition and natural law certainly have a place, and professors in Protestant Christian seminaries will look to these authorities to help determine right and wrong. Nevertheless, Scripture has the final word in Protestantism, and an ethical rule can only be binding if it is affirmed in the Bible as it is correctly interpreted. A Protestant ethicist, for example, might point to many things to argue in favor of the pro-life position, but the determinative proof that the pro-life position is pleasing to God is based on the fact that the Bible outlaws the killing of innocent human life.
Having seen this general outline of Christian ethics, it should now be clear why Christianity has produced such well-though ethical systems. Understanding Christian ethical theory and its sources can go a long way to helping others understand why Christians believe and act as they do.