Anything we say about God implicitly involves comparison. So “God exists” would be alright because the comparison there is to things which do not exist, and when only God existed, there were many things which did not exist. But other descriptions, like “God is good,” make no sense in a world where there is nothing but God. “Good” is meaningless when there is nothing that is “not-good”. “Creator” is meaningless with nothing that can be called “created”.
Why does this matter? Because it means that for attributes other than “existence,” God is dependent on Not-God. Which makes these attributes contingent, and thus not part of God as a necessary being. If they are contingent, then they are changeable. God could possibly change from good to not-good, or from creator to non-creator. Anything possible will eventually happen given enough time, and God has all eternity. The result is that anything attributed to God other than continued existence won’t last, and that has implications for placing trust in God to do anything other than be.