While this is a text that is new to me, but was in fact the original words to the tune, BUNESSAN. It is Mary Macdonald’s Gaelic Christmas song, ‘Leanabh an Aigh’ translated by Lachlan Macbean. Bunessan was actually Mary Macdonald’s birthplace on the Isle of Mull (thanks Hymnary).
Godsongs has more background as it is right in Mary’s wheelhouse.
In the New Living Parish Hymn Book we are favoured with the editor, John de Luca’s, arrangement, which has a lot more chords than usual so is worth a look. I like the diminished chord particularly. I used them all in my new backing:
1 Child in the manger, infant of Mary;
Outcast and stranger, Lord of all!
Child who inherits all our transgressions,
All our demerits on him fall.2 Once the most holy child of salvation
Gently and lowly lived below;
Now, as our glorious mighty Redeemer,
See him victorious o’er each foe.3 Prophets foretold him, infant of wonder;
Angels behold him on his throne;
Worthy our Saviour of all their praises;
Happy forever are his own.