Answer:
The clock symbolizes the passage of time and Gatsby's fear of it.
Step-by-step explanation:
The clock symbolizes the passage of time, and Gatsby wants to turn back time because in the five years since he has seen Daisy, she has married Tom and had a child. If he could destroy the clock, he would be able to turn back time. However, it is clear that Gatsby has a distorted view of time--for example, he thinks Daisy is late when she isn't (though he knows exactly how long it has been since he has seen Daisy)--and he will never be able to turn back the clock.