I think that poem is trying to say that all good things in life do not last forever, and sometimes you just have to move on. It also saying that savor and cherish the moments or times that are great and fantastic in your life and also not to take them for granted; act like that is the only happy moment you will have in your life, and then you will really enjoy it. Another main point about the poem is saying that everything in life will change, and nothing will stay or be the same.