Genesis 1:7

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.

1. God appears to use a two-step approach to creating things. In verse 6 He said, "Let there be a firmament", and here He makes the firmament.
2. This two-step approach raises the question of the purpose of the first step. Why not just skip directly to making the firmament? Possibilities I can think of are: 1) God is telling others what He intends to do; 2) It's God's way of planning; 3) When God says, "Let there be something", something actually happens that prepares the way for step two; 4) Step two is actually carried out by others, but like any good manager God gets a lot of the credit.