God, properly speaking, is existence itself. So everything that exists is somehow the result of His creative act. That being said, time itself is a creation of God’s. Time did not exist before He created it; so to say that He did nothing before He created us implies a temporal understanding of God, and the very nature of God denies such an understanding.
St. Augustine attempted to explain this:
“There was no time, therefore, when Thou hadst not made
anything, because Thou hadst made time itself” (Confessions, Book XI, chap. XIV, 17).
So, for all of time, God has been a creator.
The first man to theorize the Big Bang, a devout and holy priest named Father Lemaitre, echoed this theological position when he contended:
“If the world has begun with a single quantum, the notions of space and time would altogether fail to have any meaning at the beginning; they would only begin to have a sensible meaning when the original quantum had been divided into a sufficient number of quanta. If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time.”
This is a scientific theory that is a consequence of Einstein’s General Theory of Relativity (1917). It is instructive to see the unity of faith and reason in this instance.
So the immutability (unchanging-ness) of God holds because change is more or less a consequence of time, something that God has complete sovereignty over as Creator. He is not bound by or concept of space and time, which is the result of our presence in a universe defined by such notions. God’s existence is beyond physical explanation and beyond our ability to understand.