What the stock price says
The Gordon model allows for the fact that the market might put a price on a stock that's different from what you might estimate using the equation above. A higher stock price than predicted implies a faster growth rate than assumed, and a lower stock price implies a lower growth rate.
Again, using the above example, say that the actual stock price is $40. That implies that the expected dividend growth rate is higher than the 0% shown above. In this case, the $40 stock price, such as earnings or cash flow, implies a dividend growth rate of 5%, as $2 / (10%-5%) = $40.