The New York Times explains the split’s outcomes:

Google is proposing to have three classes of stock. Mr. Brin and Mr. Page will control the super-voting Class B stock, which have 10 votes per share and provide the two co-founders with voting control over Google. The Class B shares are convertible into the current publicly traded Class A shares, which have one vote per share and trade under the symbol Goog. Now, Google is planning to add a separate nonvoting stock called Class C shares, which will trade publicly under a separate ticker. According to Google, Class C will have all the same rights as Class A shares including the rights to dividends, if and when Google ever pays them.

As a result, if you currently own Google shares, after the stock split you will have twice the number of shares you had before, but your voting power won’t change at all as well as the value of all the shares you have.

It’s all about increasing Brin’s and Page’s power over Google’s management.