Footnote to All Prayers - CS Lewis

He whom I bow to only knows to whom I bow
When I attempt the ineffable Name, muttering Thou,
And dream of Pheidian fancies and embrace in heart
Symbols (I know) which cannot be the thing Thou art.
Thus always, taken at their word, all prayers blaspheme
Worshipping with frail images a folk-lore dream,
And all men in their praying, self-deceived, address
The coinage of their own unquiet thoughts, unless
Thou in magnetic mercy to Thyself divert
Our arrows, aimed unskillfully, beyond desert;
And all men are idolators, crying unheard
To a deaf idol, if Thou take them at their word.
Take not, oh Lord, our literal sense. Lord, in Thy great,
Unbroken speech our limping metaphor translate. 

Notes
Lewis is saying that when he prays he has images in his head of the God to whom he is praying but knows these images are totally wrong. He calls them Pheidian fancies - like the statues of Gods created by the sculptor Phidias:

Phidias or Pheidias (c. 480 – c. 430 BC) was an Ancient Greek sculptor, painter, and architect, active in the 5th century BC. His Statue of Zeus at Olympia was one of the Seven Wonders of the Ancient World. Phidias also designed the statues of the goddess Athena on the Athenian Acropolis, 

Only God knows God. So prayers fall so far short of what they should be they are like blasphemy. We are self-deceived, talking to images in our head that are not real, like counterfeit coins.

Finally he asks God to translate our prayers, the products of our limping thoughts, just as a father might translate the wishes of a small child when the child is too young to properly communicate its needs.