The title of this surah has to do with the notion that our life here on earth is short, like a fading day. Because of this, people should be concerned with spiritual matters. I'll quote this surah in full because it (like life) is very brief:
"By the fading day, man is [deep] in loss, except for those who believe, do good deeds, urge one another to truth, and urge one another to steadfastness."
This is a rather concise description of the way of salvation, according to the Qur'an.
