R.S. Thomas was a Welsh clergyman posted to a rural parish in Wales and his poetry (particularly early on) reflects this. Poems discuss the landscape, individuals and society he finds himself immersed in and how they relate to each other. He finds the farmers, though illiterate, unable to appreciate the beauty of their surroundings and incapable of a profound relationship with God, admirable simply because of their capability to scratch a life out of their hills and valleys. He also notes the changes coming to farms in Wales - famously in Cynddylan on a Tractor. Later, many of his poems discuss God, who seems to come and go from Thomas' life, causing considerable distress, even despair, when absent. Another theme seems to be reflecting on his earlier poems and earlier life.
I once tried out a few poems from this collection on a Frenchman and an American woman; they didn't appreciate it at all. It made me wonder if you have to have lived in rural Wales (as I have) to really appreciate the early works. I would still recommend this to any poetry lover - Thomas is a monument of post-war Welsh literature in English.