This is a symbol of Jay Gatsby's dreams of being with Daisy. From the book you can infer that Jay Gatsby bought his West Egg Mansion so he could see that light across the water. As we read this quote from the book when Daisy and Jay are in Jay's villa on page 93: “Compared to the great distance that had separated him from Daisy he seemed very close to her, almost touching her”. So we can see the distance between the green light and Gatsby, which was barely visible compared to how Jay and Daisy have been so close to each other all these years but didn't meet until the events of the book. Nick also represents the green light that everyone dreams of and compares him to the sailors who first settled in this country. We can read this on page 180: "I became aware of the old island here that once flourished in the eyes of Dutch sailors - a fresh and green breast of the new world." So we realize that the green light in the Great Gatsby represents dreams, whether it is about a person or the American