Which of Spivak's books? Some or many of us have not seen any of his books (although others of us certainly have - not me, though); we may like to know which is the one you are finding trouble understanding, in case we might like to obtain a copy to use for study. Is it his Calculus book which you find difficult?
All enthusiasts of Spivak's books, please give your discussions about this.
Also, something interesting - do a web search and you can find a wikipedia article on Michael Spivak.