You might want to read the Ladder of Divine Ascent by +John Climacus:
http://books.google.com/books?id=HiTaxR0EU2MC&dq=Ladder+of+Divine+Ascent&printsec=frontcover&source=bl&ots=T7HeWcOtQm&sig=nFSkuCzoNiLWeTg9IHC0RqqJEgI&hl=en&ei=UHu2SunSE9Kv8Qadzfm5Dg&sa=X&oi=book_result&ct=result&resnum=16#v=onepage&q=&f=false