exposure

• 'Our brains ache, in the merciless iced east winds that knive us'

  Personification creates a sinister tone from the start and establishes nature as the true enemy. 'brains ache' - pain physically and mentally. 'Our' - universal experience.
• 'But nothing happens'

  Refrain emphasises the futility of war. Conjunction shows the defiance of expectation - people expect war to be all bloodshed and fighting, but the somewhat harsher reality is boredom and fear of the unknown -AO3 - Owen had a first hand experience of this.
• 'What are we doing here?'

  Rhetorical question - in their 'dull' pain, the soldiers have lost their purpose - of patriotism and pride.
• 'The poignant misery of dawn begins to grow'

  Oxymoron - even in the 'poignant' beauty of 'dawn', there is 'misery.' Even in a new day, there is no hope. 'Begins' shows that this is just the beginning - there is more to come. 'Grow' means it gets worse every day, as more lives are lost, to the 'sudden successive flights of bullets', but mostly to the 'mad gusts'
• 'We only know that war lasts, rain soaks and clouds sag stormy'

  Pathetic fallacy emphasised by the triadic structure highlights the repetitive misery of war. 'Only' - they cannot think of anything else.
• “slowly our ghosts drag home: glimpsing the sunk fires”

  Literally - they have died and their ghosts are returning home to see their loved ones. Metaphorically - war has changed them: they are now only a 'ghost' of what they once were. 'Slowly - adverb links back to 'war lasts.' Verb 'drag' shows how hard it is for the soldiers to return to the homes and families they love, after the traumas they have experienced. AO3 - this is sad really, as Owen never returned home
• 'Crusted dark-red jewels'

  Metaphor- frozen blood described as jewels - poet sees men's lives as valuable and ultimately, wasted
• 'For love of God seems dying'

  It is clearly very hard to keep 'love of God' love suffering. AO3 - Owen initially pursued a career in the church, but gave up when he felt the church had failed to care for those in its locality - church has done nothing to help soldiers. Through this, and his critical tone throughout, I can tell that Owen is very anti-establishment
• “we hear the mad gusts tugging on the wire,

  Like twitching agonies of men among its brambles.”