In  Gen 1:6 why were the waters devided?
Because up to Gen 1:14, every 'let there be' was a 'remedial' step.

Gen 1:2-3 
	
>2 And the earth was without form, and void; and darkness was upon the face of the deep.   
3 And the Spirit of God moved upon the face of the waters.	
>And God said, Let there be light: and there was light.

Gen 1:6
>6 And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters.  
7 And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.

Gen 1:14-15 
>14 And God said, Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years:  
15 And let them be for lights in the firmament of the heaven to give light upon the earth: and it was so.

Gen 13:8, etc.