The object of philosophy is the logical clarification of thoughts
what the poet is called upon to clarify is not answers ...
One is a question of sense, the other a question of sensibility; and both employ the diction of precision, and it's method: for Wittgenstein, this being the sense, reference and logic of Frege; and for Levertov, it is the image reconcieved through imagism - clear and not occluded by some neccessary symbolic obscurity, and intermingled with the poetics of Mallarme filtered through the vernacular of William Carlos Williams.
Thus for both: When questions are as clear as possible, and no less; the question answers itself; and what are not questions negates itself - becomes merely historical, and no longer alive for us; the question then being whether this compelling clarity, which compels by virtue of its transparency is attainable.
This book will perhaps only be understood by those who have already thought the thoughts already expressed in it - or similar thoughts
Wittgenstein is indulging in a little paradoxical play; for if one has already 'thought the thoughts', why read the book - it is an irrelevance - time lost, or buried; or at best, a recapitulation; in fact, he is referring to Platos Meno, where Socrates demonstrates that knowledge (even new knowledge), is in a sense, recollection; or perhaps, dia-logos is una-logos.
But this does not only go for thought, for sense; it is true also for sensibility - as noted by Mahmoud Darwish: (poetic) sensibility reacts only on (poetic) sensibility.
It's also noted by Hegel in the Phenomenology, where he moves from Sense Certainty (ie sensibility) to Absolute Knowledge.
The task of the poet is to make clear to himself, and thereby to others, the temporal and eternal questions.
Eternal questions which are not temporal, are not of the world; for example the questions of mathematics; temporality, being in time, is being in the world; and when eternal, reoccur from generation to generation, are then questions of natality, of eros and mortality; and their reverse; in Russell's phrasing in the preface, they are:
The questions of life
Questions which he suspects Wittgensteins method hardly touch on; and which Levertov glances at directly, but through a 'mist' darkly, and by her poetics of lyrical confrontation.
The following is a response to the comment below:
It's not a criticism but a condensed description: Levertov was known for 'confronting' political themes, particularly the Vietnam war - she wasn't allusive; and also because she isn't a confessional poet in the style of Olds or Plath; like Shelley, she confronted large themes; she had a late turn towards religous themes, an image of which was a mountain shrouded in 'mist'; and it was towards Christianity, the religion she had been brought up in after her fathers conversion from orthodox hassidic Judaism - hence the biblical reference to 'through a mirror darkly'; actually she wrote an essay which elaborates on the quote from Ibsen, and on her poetics - which I only discovered after writing this; and is worth reading.