Full Idea
One should step up from physical beauty, to moral beauty, to the beauty of knowledge, until at last one knows what absolute beauty is.
Clarification
'Beauty' is the Greek word 'kalos', which also translates as 'fine'
Gist of Idea
Progress goes from physical beauty, to moral beauty, to the beauty of knowledge, and reaches absolute beauty
Source
Plato (The Symposium [c.384 BCE], 211c)
Book Reference
Plato: 'The Symposium', ed/tr. Hamilton,W [Penguin 1951], p.94
A Reaction
Presumably this is why Socrates refused sexual favours to Alcibiades. The idea is inspiring, and yet it is a rejection of humanity.