A firmament means an expanse. This is the atmosphere, space, if you like.
When you think of the planning which went into the creation of the world and the creation of man, just think of the planning of God in our individual lives. You look back and say, ‘See how many things God prepared me for years before. And if I thought about it, I wouldn't be able to figure out why God put me through this experience, or that experience, but as the years go by, it becomes obvious, and you see the preparation.