What metaphor does king use to close the letter, and why is it appropriate?

From the text:

Let us all hope that the dark clouds of racial prejudice will soon pass away and the deep fog of misunderstanding will be lifted from our fear drenched communities, and in some not too distant tomorrow the radiant stars of love and brotherhood will shine over our great nation with all their scintillating beauty.

This metaphor is completely appropriate to King's argument in that it provides hope and new beginnings. The bulk of the letter concentrates on the painful truths of racism and segregation..... and ends by looking at a future free of the darkness.