When it is said
It stands among the prayers for April in the Leonine Sacramentary, a book of Roman Mass prayers.
Later Roman books, the Roman Missal and the Church of England’s Book of Common Prayer all set it for the third Sunday after Easter.
The scholar William Bright read it as a prayer for those baptized on the night before Easter.
Anyone may pray it at home for someone who has wandered from the faith.
Where it comes from
No author known
Where it comes from
The Leonine Sacramentary is kept in the cathedral library at Verona, in Italy. The manuscript was copied early in the 7th century, although much of what it holds is older. Joseph Bianchini found it there and first printed it in 1735.
Charles Lett Feltoe, Sacramentarium Leonianum (Cambridge, 1896)
Why is it called Leonine?
Scholars once named Pope Leo the Great (died AD 461) or another early pope as the book’s author. Charles Feltoe edited it in 1896 and kept the familiar name. He judged the book a 7th-century collection of older prayers that no pope could have made for public use.
Charles Lett Feltoe, Sacramentarium Leonianum (Cambridge, 1896), the introduction
In Latin
Deus, Qui errantibus, ut in viam possint redire,
veritatis lumen ostendis;
da cunctis qui Christiana professione censentur,
et illa respuere quae huic inimica sunt nomini,
et ea quae sunt apta sectari.
Per.
From the Leonine Sacramentary, as William Bright printed it in Ancient Collects (1864).