Near the end of the novel Gatsby tells one of his servants not to drain the pool as planned. The summer is over - as is the story of the novel and Gatsby's hopes as well - and Gatsby has yet to use the pool. Before it is drained, he wants to use it once. 

In this context the pool can be seen to represent an idea that Gatsby has not been enjoying his wealth. He has been living in and for his vision of marrying Daisy. As that fantasy is coming to a close, he realizes that in the real world time is moving on. 

His decision to use the pool suggests that his fantasy is ended.

Later on the same day he is killed. 

Gatsby's book of resolves is a demonstration of his character. A person of impressive innocence, we can see the source of Gatsby's tenacious dreaming in the determinations he made for himself as a young man. The resolves are modest, insistent, and practical. 

Like the example of the pool, we see Gatsby's connection to reality in the book of resolves. Yet we also see his ardent nature. This can be seen as what allows him to dedicate himself so fully to a dream. We see in the resolves also a deep urge toward self-improvement and a belief that these improvements can be made.