"Earthly knowledge is but a shadow."
To see the Ideas alone is real knowledge. Relativistic knowledge - Arithmetic (Time) and Geometry (Space) are quite meaningless in themselves.
Plato's allegory of the cave is well worth reading (this is a summary):
The things of this world which our senses perceive have no true being; they always become, they never are: they have only a relative being; they all exist merely in and through their relations to each other; their whole being may, therefore, quite as well be called a non-being. They are consequently not objects of a true knowledge, for such a knowledge can only be of what exists for itself, and always in the same way; they, on the contrary, are only the objects of an opinion based on sensation. So long as we are confined to the perception of these, we are like men who sit in a dark cave, bound so fast that they cannot turn their heads, and who see nothing but the shadows of real things which pass between them and a fire burning behind them, the light of which casts the shadows on the wall opposite them; and even of themselves and of each other they see only the shadows on the wall. Their wisdom would thus consist in predicting the order of the shadows learned from experience. The real archetypes, on the other hand, to which these shadows correspond, the eternal Ideas, the original forms of all things, can alone be said to have true being (οντως ον), because they always are, but never become nor pass away. To them belongs no multiplicity; for each of them is according to its nature only one, for it is the archetype itself, of which all particular transitory things of the same kind which are named after it are copies or shadows. They have also no coming into being nor passing away, for they are truly being, never becoming nor vanishing, like their fleeting shadows. Of these only can there be true knowledge, for the object of such knowledge can only be that which always and in every respect (thus in-itself) is; not that which is and again is not, according as we look at it.