Terrific movie. Beautiful message. I've seen many reviewers say it's depressing, but I found it to be the exact opposite.
Joe is a representation of an average person. We chase after the moment where our life makes sense. Where everything we have done amounts to something. Like getting a new job, a promotion, moving somewhere new, etc. For Joe, his moment was getting in to a popular jazz group. And then he did. And for a moment, he was happy.
But then towards the end of the film, he does the performance. His mother comes to support him, he has the time of his life, but then it's over. And he's standing outside the jazz club and he realizes he isn't happy. And he's thinking 'Why am I not happy? This was my purpose in life, the thing I've been chasing after and I finally got it. Music is my spark, my purpose. But why am I not happy?'.
Later on in the film he learns something. Your spark isn't your purpose. He's confused because he thought music was his purposeโ but now he doesn't know what it is. But by the end of the film, he figures it out.
The purpose of life, is just being alive. Living every moment and appreciating that fact. Real clarityโ real PURPOSE is found when you stop running after a purpose. When you stop and look around you, your purpose will come on its own. Because it isn't some set path, destiny or fate that decides your purpose. The only purpose is living every moment to the most. By laying on a vent and laughing at the feeling, staring at the sky and seeing the colors, listening to a musician on the subway, or holding the seed from a tree. THAT is the purpose. The meaning of life is just that. Being alive.