Gatsby, who once had a great and wonderful past tried to get it back. He lived his whole life working for it, gave everything for that wonderfully wretched past. And how his life ends, perfectly shows how it can't repeat. Where before that life ends, he already had a fortune that he hadn't looked at just because he'd been looking at his past persistently. And that past had ruined his life, too. Just because he kept that hope very severely.
The past can't repeat. Stop wishing for it. Instead, live your present and let the past be your sweet memories. That you can recall whenever present hits you hard and you feel like losing yourself. I guess that's what past is all about. Atleast, that's what James Gatsby had taught me very deeply.