Niles and Merton met via mutual friends - Victor Hammer and John Howard Griffin - and became friends. Niles was interested in setting some of Merton's poems to music. Merton said fine, and from this came the Nile-Merton Song Cycle. Most of the work was done after Merton's death in 1968.
Below is a lecture / performance of 8 of these poems at Villanova University in 2016. I've started the video at where the performance begins, skipping over the lecture.
I'm not sure that the "ballad" fits Merton's poetry, or Merton's poetry fits the ballad. It seems to me that Merton's poetry reaches for something beyond words, much like the song of the Negro ditch digger, Objerall Jacket.