One possible interpretation of the song, perhaps not intended by the songwriter, is that it reflects the relationship between W B Yeats, the great Irish poet, and his mistress and muse, Maud Gone. Yeats' words have long since become part of the Irish psyche. In a poem about 1916 he wrote, "A terrible beauty is born". Gonne was an ardent Nationalist and a catholic. Yeats was an Irish Protestant. Gone repeatedly refused his entreaties to marry, partly, she said, because he didn't feel like her about Irish nationalism, partly because he would not become a catholic, but mainly because she felt that Yeats needed his sorrow and unrequited love to inspire his writing
Certainly much of his work, both poetry and plays, was inspired by, and addressed either directly or indirectly to, Maud Gonne. A good example is the poem, "Aedh Wishes for the Cloths of Heaven". It contains the lines, " I have spread my dreams under your feet/Tread softly for you tread on my dreams.".
In 1916 he wrote in the poem, "No Second Troy", "Why should I blame her that she filled my days/With misery, or that she would of late/Have taught to ignorant men most violent ways/Or hurled the little streets upon the great.".
And the connection with the Christy Moore song? A Yeats poem, "Under Ben Bulben", ends with the words, "Cast a cold eye/On life, on death/Horseman, pass by!".
Yeats won the Nobel Prize for Literature and died in 1939. His simple gravestone near Ben Bulben in County Sligo carries only his name and dates and the words
Cast a cold eye
On life, on death
Horseman, pass by!