Full Idea
If the world is beautiful and its maker good, he had an eye on the eternal; if not, on that which is subject to change; clearly the world is the fairest of things, and he the best of causes, so it is eternal.
Clarification
'Beauty' is the Greek word 'kalos', which also translates as 'fine'
Gist of Idea
Clearly the world is good, so its maker must have been concerned with the eternal, not with change
Source
Plato (Timaeus [c.362 BCE], 29a)
Book Reference
Plato: 'Timaeus and Critias', ed/tr. Lee,Desmond [Penguin 1971], p.41