"Thus the writer who wisely tells us of the birth of the Universe does not fail to put these words at the head of the narrative. "In the beginning God created;" that is to say, in the beginning of time. Therefore, if he makes the world appear in the beginning, it is not a proof that its birth has preceded that of all other things that were made. He only wishes to tell us that, after the invisible and intellectual world, the visible world, the world of the senses, began to exist."
-St. Basil of Caesarea, Hexaemeron, Homily I
If "In the beginning God created," the presupposition must necessarily be that God existed even before time itself, in a manner of existence which must be beyond our understanding. This means that God does not "change" nor is subject to change, but works within the universe of time from outside of it.
We perceive God in time because we are created beings, but God Himself is beyond the beginning and end of things; He knew exactly that Adam would sin, and when he did sin God knew exactly how He would redeem humanity. He knows exactly what will become of each and everyone of us because all of time and space are held in His hand.