God does not change, because to change would imply that he is not perfect. That he is perfect means that he is the good itself. Goodness is diffusive of itself, that is, it wishes to impart goodness to other beings. To be is better than not to be; being and goodness are one and the same. Therefore, since God is goodness itself, and since goodness wishes to impart its goodness to other beings, the eternal, unchanging will of God would be to create other beings to share in his goodness, which would necessarily be limited in time and extension, since an effect cannot exceed its cause.
-ACEGC