Full Idea
We agree the gods are happy, and no happiness is possible without virtue: there is no virtue without reason: and reason is associated only with the human form: then it must follow that the gods themselves have human shape.
Gist of Idea
The gods are happy, so virtuous, so rational, so must have human shape
Source
M. Tullius Cicero (On the Nature of the Gods ('De natura deorum') [c.44 BCE], I.48)
Book Reference
Cicero: 'The Nature of the Gods', ed/tr. McGregor,Horace [Penguin 1972], p.89