Full Idea
It is impossible for God to be immoral and not to be the acme of morality; and the only way any of us can approximate to God is to become as moral as possible.
Gist of Idea
God must be the epitome of goodness, and we can only approach a divine state by being as good as possible
Source
Plato (Theaetetus [c.364 BCE], 176c)
Book Reference
Plato: 'Theaetetus', ed/tr. Waterfield,Robin [Penguin 1987], p.73