that it is a long book.

就是这是一本很长的书
Not the longest book you will ever read, but long enough.

虽然不是你们所读过的最长的但是也够长了
In fact, in part, because of this,

事实上某种程度上正因为如此
we are only reading approximately half the book,

我们只会阅读大约半本书
the first five books, to be more specific.

更具体地说是前五卷
the first five books that deal with and culminate in the best city,

前五卷探讨了最好的城市
Plato's ideal city, what he calls Kallipolis,

柏拉图的理想之城他命名为Kallipolis
the just city, the beautiful city, ruled by philosopher-kings.

是由哲学王管理的公正之城唯美之城
The second half of the book turns in somewhat different,

这本书的后半部分多少转向了不同的领域
certainly equally important directions,

当然有着同等的重要性
but would take us much more time

但是需要更多的时间
than the time we have allotted to deal with.

远远超出分配给我们的时间去处理它