I think the hundreds of reviews preceding this one sum up the book pretty well, so I won't recap it all here. I just wanted to point out that the reviewer who thought that Flatland was a religious allegory, with the Sphere as Jesus has defintely missed the point - Sphere is one of a line (no pun intended) of all too fallible and very much human characters who we meet in the book, illustrating one of its sharpest ironic points (I just can't help myself now).
The first is the Point, utterly convinced, in the teeth of all the evidence, of the non-existence of everything but itself. Then we meet (in a dream) the King of Lineland, who prefers to believe that the Square is a mutant woman, rather than believe in a two-dimensional space (I promise I'm not making this up). Then we have A. Square, our narrator, who has to be forced to accept the reality of three dimensions by being forcibly removed from Flatland.
And, almost at the end of the book, the Sphere, who, until now has seemed to represent enlightened wisdom, shows his own flaws, by reacting angrily and petulantly to the suggestion of fourth, fifth or higher dimensions.
The Sphere is definitely not meant to be divine - he's just as limited in vision as all the other characters. I hardly think that a clergyman would be so unflattering about Jesus.