This is an Advent song with a fine old hymn tune. It is from a Latin original Instantis adventum Dei by Charles Coffin and translated by Robert Campbell. It is set to OPTATUS VOTIS OMNION of unknown authorship but collected in the George Radcliffe Woodward, edited, Songs of Syon. It is all public domain.
The text is here and you could purchase the sheet music at OCP.
I tried a different mix of fake organ sounds in BIAB:
This is the sheet music with a different text.