Augustine of Hippo

Do not ask what truth is. For mists of corporeal images and clouds of phantasms will rise forthwith and confuse the clarity that flared up in you in a first impulse when I said: 'truth.' When the word 'truth' is spoken, remain if you can in the first impulse which struck you as a flash of lightning. But you cannot. You fall back into this world of familiar, earthly things.

-De Trinitate