Gillian Clarke, in her poem "Lament," has a strong message for her reader.
The setting of the poem is during the Gulf War in 1991; it is based upon photographs from the media that showed how terribly life was impacted by war, starting from the very foundations of earth, nature (including the oceans and the animals), and progressing to human beings (the soldiers and the natives who have joined the war effort).
A lament is a way of grieving or mourning, in this case, written as a poem. The word "for" used at the beginning of the line indicates one of the things for which Clarke mourns in reviewing the haunting images. This poem is first and foremost, a way for Clarke to express the horror visited upon the land and people in the advent of war.
Three things that Clarke mentions specifically in the poem are:
"For the ocean's lap with its mortal stain" which refers to blood spilled in the ocean.
"For the soldier in his uniform of fire" refers to a soldier who has caught fire.
"For...the ashes of language," according to Clarke, refers to the words of peace that might have ended the war, which have been destroyed.