It implies a book that is easy to accept as “sweet” but not so easy to digest, nor is the message really simple good news as is first assumed. It could be argued, I suppose, that that “little book” is the New Testament” of the bible.
Not saying I believe that, but when it comes to the book of Revelation, there is a LOT of symbolism and even experts can strongly disagree on the meaning of verses.
I know that those in the know approach Revelations with care and that interpretations vary quite a bit. However, the “little book” does appear at or near the last days, it is sweet (attractive) but upsets one who takes- (it in even makes the one who ingests it sick.) Any rate thanks I do not insist on my reading.