The music is by Mike Scott of The Waterboys. The words are by William Butler Yeats (and George Moore).
A song from the play Cathleen ni Houlihan (1902), sung by the Poor Old Woman:
They shall be remembered for ever,They shall be alive for ever,They shall be speaking for ever,The people shall hear them for ever.From "The Blood Bond," a song from the play (1901), by Yeats and Moore, lines sung by Diarmuid:
Let the sea bear witness,Let the wind bear witness,Let the earth bear witness,Let the fire bear witness,Let the dew bear witness,Let the stars bear witness![Texts from William Butler Yeats, The Poems, ed. Richard J. Finneran (New York: Macmillan, 1983), 537, 538.]