Letters are the means by which G-dly energy enlivens existence. Not only the words and the font of the letters in Loshon HaKodesh, but also the ideas behind them. 

That means that, “May there be a sky,” includes all the details of what makes up a sky. Those particular ideas, which are subcategories of the general idea, are made of letters too. For example: the storehouse of snow, the grinders of mann for the tzaddikim, etc.