What is the poem your heart leaps up about?

William is talking about his connection with nature. He's so passionate and understands it so well he says he wants that connection till he's an old man, and if he doesn't have that connection, he would rather die. Then Wordsworth goes on to say that children have a better feel for nature then older people do, he feels they are superior and in a higher rank then adults. Kids have a natural bond with nature.