Morality means choice. Choice means priorities. Priorities mean a hierarchy. A hierarchy means something at the top, a standard. That is the greatest good. If you have no greatest good, you have no hierarchy, you have no priorities. If you have no priorities, you cannot make intelligent choices. If you cannot make intelligent moral choices, you have no morality. You can still guide your life by your feelings or by social fashions, but that is not choice – not free, responsible, moral choice. Both feelings and fashions push you; you are passive. But moral choice is your own doing; you are active. You are responsible for your choices but not for your feelings or for your environment’s fashions.
Peter Kreeft, Making Choices: Practical Wisdom for Everyday Moral Decisions