Of old you laid the foundation of the earth,
and the heavens are the work of your hands.
They will perish, but you will remain;
they will all wear out like a garment.
You will change them like a robe, and they will pass away,
but you are the same, and your years have no end. (Psalm 102:25-27, ESV)

So when God desired to show more convincingly to the heirs of the promise the unchangeable character of his purpose, he guaranteed it with an oath, so that by two unchangeable things, in which it is impossible for God to lie, we who have fled for refuge might have strong encouragement to hold fast to the hope set before us. We have this as a sure and steadfast anchor of the soul…. (Hebrews 6:17-19, ESV)

Article I - There is Only One God

We all believe with the heart and confess with the mouth that there is one only simple and spiritual Being, which we call God; and that He is eternal, incomprehensible, invisible, immutable, infinite, almighty, perfectly wise, just, good, and the overflowing fountain of all good.

Created things have a beginning and an ending, but not so their Creator. The answer to the child’s question “Who Made God?” is simply that God did not need to be made, for he was always there. He exists forever, and he is always the same. He does not grow older. His life does not wax or wane. He does not gain new powers nor lose those that he once had. He does not mature or develop. He does not get stronger, or weaker, or wiser, as time goes by. “He cannot change for the better,” wrote A. W. Pink, “for he is already perfect; and being perfect, he cannot change for the worse.”

The first and fundamental difference between the Creator and his creatures is that they are mutable and their nature admits of change, whereas God is immutable and can never cease to be what he is.