Remember how we learnt about resonance in the ninth grade? How objects on a piano would vibrate when a particular note was played? Because that note was their resonant frequency..
I think the whole point of art is to find that resonant frequency in people. Like when you're moved by a sad song, or a beautiful painting, or a brilliant piece of writing. It's because that song, or painting or poem has found your resonant frequency.
And that's what separates great art from the rest. Good art can find the resonant frequency in a few people. Maybe a lot of people in a single generation. But as times and people change, merely good art remains rooted in its generation and fails to move.
That's what separates good art from great.
Great art can find that resonant frequency in almost every single person. Generation after generation. Which is why 400 years after he died, teenagers are taught Shakespeare in school. Not just because he wrote well; there are a plethora of good writers. But because his writing reflects who we are, and every single person can see a himself in his work. That's why we're struck by the beauty of a Vermeer, while wondering how a van Meegeren could ever have passed for one.
Eternal. That's what great art is.