if everything happens that can't be done
Our speaker starts off questioning the intelligence of books and teachers, introducing the gleeful language that runs throughout the poem. We're on shaky ground here, grammar-wise, but we're up for the challenge.
Then the poem moves on to a discussion of what "one" is, and plays with language a bit. It breaks down boundaries between the large and small parts of our world, and continues to question the ability of books to describe the world. That's when we start getting into the meat of the impossible happening, when the poem claims that "forever was never till now." Minds? Blown.
The speaker then get an idea of where this exhilarated mood might come from. Yep, our speaker is in love. He describes this love as greater than books, or really anyone, can describe. Sounds about right.