Ecclesiastes 12:7- The Spirit
Then shall the dust return to the earth as it was: and the spirit shall return unto God who gave it. Eccl.12:7
All throughout the book, the preacher reminds us that everything is ephemeral, transitory, and vanishing like a vapor. However, towards the end of the book, at the point where he describes how the strong human gets weaker, ultimately falling to the ground, he mentions that there is one part of man that isn't a vapor after all: the spirit of man.
It is certainly foolish to ignore the spirit and focus all attention on things that are intrinsically vaporish and perishing. Jesus asked what would it profit if a man gained the whole world but lost his on soul. Nothing.
Therefore, we are reminded to remember our creator in the days of our youth.