Answer: The parallelism emphasizes the speaker's Irish nationality.
This is a poem by W. B. Yeats, an Irish poet, and it describes the feelings of an Irish soldier fighting during WWI. The poem uses parallelism in the phrases "My country is Kiltartan Cross" and "My countrymen Kiltartan's poor." Kiltartan Cross is a place in Western Ireland, and the poet uses this parallelism in order to highlight how strongly the speaker feels about his Irish nationality.
