God is omnipotent, therefore no good can be lacking in Him (if He were destitute of any part of His nature, He would not be all-mighty). He is so good that there is no mixture of anything un-good in Him, whereas everything beside Him is lacking in some good.
Nothing can be so supreme an evil as God is supreme goodness. He is all good and unmixedly good. None is good but God: a goodness, like the sun, which has all light and no darkness.
From the book “Boundlessly Good”