"the light of the body is the eye"

This is incorrect. Eyes absorb light and produce electrical signals interpreted as vision by the brain. Further, it seems to me that the set of thing that 'the light of the body' describes is an empty set; there's no literal interpretation (our bodies do not shed visible light) and there's no construction similar enough that suggests an interpretation (the X of the body / the light of the X). "The light of the sun" / "The light of the moon" is the closest I can find and both of those suggest the literal interpretation.

Originally, I was going to do a very charitable reading: invent a sane meaning for "The X of the Y is the sub-Y" as "sub-Y is how Y handles/uses/interpets/understands X" and say that goals, as subparts of an agent, are how an agent understands its rationality - perhaps, how an agent measures their rationality. Which is indeed how we measure our rationality, by how often we achieve our goals, but this doesn't say anything new.

But when you say things like

You don't understand ... Maybe you'd get more out of ... You may be misinterpreting

as if you were being clear in the first place, it shows me that you don't deserve a charitable reading.