The moral of this sentence is that life is like the end of a day, and time passes quickly. We should cherish the present time and don't let it go to waste. At the same time, it also implies that when we face beautiful things, we should learn to cherish and be grateful, because they may soon disappear.
In short, the sunset is the end, and the sunset glow is also a philosophical word, reminding us to cherish the present time and be grateful for the beauty in life.