A sonnet from CS Lewis - but what does it mean?

I was intending to blog on all this week's amazing stem cell stories tonight but have run out of time. It will have to wait.

Anyway for something completely different here is one of my favourite poems (a sonnet) from CS Lewis from one of my favourite books 'The Pilgrim's Regress'

The book is obviously based on Bunyan's 'Pilgrim's Progress' but the chief character, instead of meeting people who represent different vices and virtues encounters characters embodying different philosophies.

See if you you can work out what it means and whether or not you approve of the theology?

A clue - it's titled 'The footnote to all prayers'

It's an earlier version - the later one in the Regress is tidied up and a bit tighter in the wording. Lewis obviously went back to it.

He whom I bow to only knows to whom I bow
When I attempt the ineffable Name, murmuring 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 unskilfully, beyond desert;
And all men are idolators, crying unheard
To a deaf idol, if Thou take them at their word.
Take not, O Lord, our literal sense. Lord, in thy great
Unbroken speech our limping metaphor translate.