This old saying is used to mean to say that beauty is not universal but relative, that a man will see one thing as beautiful while another man will see that same thing as ugly. But, to my understanding, it is not that beauty is relative but that not all men understand beauty, so, while it would appear that beauty is subject to opinion, it is actually a case of the understanding of beauty that is subject to opinion. Beauty is in goodness, and this is why not everyone understands beauty. For one man may see a plain person for who he is, not how he looks, and so call him beautiful, a person, while another man will see that same person for what he looks like, not who he is, and so call him ugly, less than a person. Another example is that a man will be called beautiful for his virtues by some and ugly for his faults by others. Yet another example is that the world will be called beautiful by an optimist, for he sees everything with hope and optimism, while the world will be called ugly by a pessimist, for he sees everything with despair and pessimism.
Moreover, since beauty is in goodness, and we all know what beauty is but do not all understand it, tha beauty must not be born in the human mind but in something else. It could be said that it is born in goodness itself, that true beauty is virtue, personhood, hope, and other good things, but beauty cannot be these things because they are able to change. Beauty cannot change because it is universal. If something universal could be changed, than it would not be universal but relative. For example, if man was not always and everywhere man, than a man could change himself into something else, however that might happen, but since man is universally man, than he cannot change his nature as man. Since beauty cannot change, than its origin must be something else that cannot change. This cannot be the Universe, or the laws therein, because these things are all subject to change, whether naturally or supernaturally. So beauty’s origin must be outside the Universe. I believe that its origin is not only with God but that God is Beauty Itself.