A Poem is a Letter to God
A poem is a letter to God. Its meaning does not need to be clear to the poet or to the reader, for it is clear to God. It is more an act of homage - a sacrifice - literally - a 'making holy'.
As the reader we enjoy its mystery, just as we enjoy participation in ceremony - feeling part of something bigger than us. Only the fool would expect to fully drain the poem of its meaning - leaving themselves with only an empty shell - the merely literal.
After writing this I came across this similar thought by Joseph Brodsky:
"…after all, any art is essentially prayer. Any art is directed to the ear of the Almighty. Herein, actually, lies the essence of art. That's for certain. A poem, if it's not a prayer, then it's at least put in motion by the same mechanism as prayer."
From Solomon Volkov's Conversations with Joseph Brodsky