What makes a thing good?
A thing is good when it attains the purpose for which it was made. I have before me now a watch. Is it a good watch? How will I know whether it is good? By asking what the purpose of a watch is. The purpose of a watch is to keep time. Does it keep time? Yes. Therefore, it is a good watch. Now let us apply that to our ultimate end. Why were we made? What is the purpose of living? The purpose of living is to be supremely happy. How do we become supremely happy? By attaining the life and truth and love which is God.