What is Mishima trying to convey/teach us about beauty in his novel, The Temple of the Golden Pavilion?

Beauty presents a paradox: the ideal is sublime and even ethereal, but it must have an earthly manifestation in order to be understood by human consciousness. But the real can never match the ideal so all earthly manifestations of the highest beauty are bound to disappoint.
This is the paradox that Mizoguchi faces. For his father, the Golden Temple is sublime. He knows himself to be unattractive so there is no chance of any contest. The real Temple is bound to disappoint.
Father Dosen only compounds his problem. Anticipating a lifetime serving the Temple, when the Father does not choose him, Mizoguchi must condemn the Temple: it has failed him, he reasons, he has not failed it.
Liberation from the burden of his duties (which he refuses to admit he neglects) and from the failed perfection of the Temple are joined in his twisted but staunch resolve: he burns down the Temple, and in doing so feels free.