When it is said
The Old Gelasian book sets it among the prayers for the sixth Sunday after Easter week.
The Church of England’s Book of Common Prayer of 1662 makes it the prayer for the first Sunday after Trinity.
It is short enough to say at any moment when your own strength runs out.
Where it comes from
No author known
A prayer of the Church of Rome
The prayer is one of the older prayers of the Church of Rome, gathered into a book of service prayers that was probably put together near Paris about AD 750. That book, the Old Gelasian Sacramentary, is the second oldest of its kind to survive in the West.
H. A. Wilson, The Gelasian Sacramentary (Oxford, 1894), page 106; The Cult of Saints in Late Antiquity database, University of Oxford, record E07005
A book older than Charlemagne
The Old Gelasian book survives in a manuscript in the Vatican Library, one of the few Western service books left from before the days of Charlemagne. It carries the name of Pope Gelasius, who lived in the 5th century, but the link to him was made later and is false.
H. A. Wilson, The Gelasian Sacramentary (Oxford, 1894), introduction; Wikipedia, “Gelasian Sacramentary”
What the words mean
Close to the Gospel
The prayer’s reason for asking, that without God our weakness can do nothing, echoes the words of Jesus when He called Himself the vine and His disciples the branches, “Apart from Me you can do nothing” (John 15:5).
The Scripture in it
I am the vine and you are the branches. The one who remains in Me, and I in him, will bear much fruit. For apart from Me you can do nothing.
Bible text: Berean Standard Bible, public domain.
In Latin
Deus, in te sperantium fortitudo,
adesto propitius invocationibus nostris;
et quia sine te nihil potest mortalis infirmitas,
praesta auxilium gratiae tuae,
ut in exequendis mandatis tuis
et voluntate tibi et actione placeamus.
Per Dominum.
From the Old Gelasian Sacramentary, Book I, section 62, ed. H. A. Wilson (Oxford, 1894), page 106.