I’m looking at hymns from the Australian Catholic Worship Book, that I haven’t covered from other sources to date.
This is the Benedictine nuns of Stanbrook Abbey’s translation of of the c4 Nunc sancte nobis Spiritus, attributed to St Ambrose. It is from the Liturgy of the Hours.
It Is here set to NIAGARA by Robert Jackson.
I’ve seen a few settings suggested, but chararacteristically for CWB I, none suggesting this one. Similarly, this text is not listed by Hymnary as being set to this tune. Call the editors idiosyncratic with their matching of text to tune.
CWB I places the tune in the key of G rather than Ab as below, thanks be to God.
The text is here.

I want to call the editors more than just idiosyncratic…