Morality is the quality of human acts that render them good or evil. And the morality of the act is usually judged with respect to our ultimate end or goal in life. Any act that helps us attain our ultimate end is good; and any act that hinders us from attaining our ultimate end is evil.
Every person, whether he or she realizes it or not, has an ultimate end – the goal to which all goals are directed. For Catholics the ultimate end is God Himself. So, for a Catholic, any act that helps him or her attain union with God is good; any act that hinders him or her from union with God is evil. Usually the system of morality and code of conduct that a Catholic goes by is formulated by human reason aided by Divine Revelation.
What about a person who does not believe in God? A person who does not believe in God also has an ultimate end, for example, natural happiness. Therefore, any act that helps him or her attain happiness is good; any act that hinders him or her from attaining happiness is evil. His or her system or morality and code of conduct will be dictated by human reason unaided by Divine Revelation.
Is it possible to have morality without reference to God? Yes. In fact, there have been people who devised their system of morality without God. Confucius is one example. However, there is a serious risk involved when a person formulates a system of morality based solely on reason unaided by Divine Revelation. For example, the person could make a mistake in figuring out in what his or her ultimate end consists. The person might think that ultimate happiness consists in wealth, or power, or pleasure instead of God. If this person makes a mistake on this fundamental question, he or she can end up with a code of conduct that – from the Catholic’s standpoint – is very immoral.