When it is said
In the Gelasian Sacramentary it is the prayer after Communion at a Mass for peace.
The Book of Common Prayer of 1549 set it for every morning of the year.
It is short enough to pray at any hour, whenever the news is of war.
Where it comes from
No author known
From a Roman Mass for peace
The prayer comes from the Gelasian Sacramentary, a Roman book of prayers for the Mass. Among its prayers for peace it is the one said after Communion. Its one surviving copy was made about AD 750 in the Frankish lands, from older Roman prayers, and it is now in the Vatican Library. The book bears the name of Gelasius (bishop of Rome from AD 492 to 496), but no writer is named for the prayer.
H. A. Wilson, The Gelasian Sacramentary (1894), book III, 56; The Cult of Saints database, University of Oxford, record E07005; William Bright, Ancient Collects (1864), the appendix
Into English in 1549
The old Salisbury service book set it for the morning office. In 1549 the first Book of Common Prayer put it into English as the second collect, or set prayer, at morning prayer. By the book’s own rule, this prayer and the one after it never change and are prayed every day of the year.
William Bright, Ancient Collects (1864), the appendix; Edward Cardwell, The Two Books of Common Prayer (1852), Matins of 1549
What the words mean
To serve You is to reign
In the Latin, God is the One Whom to know is to live and Whom to serve is to reign. The 1549 English turned the second line into “whose service is perfect freedom”. In his 1864 book of old Latin prayers, the scholar William Bright listed it among the important changes the English made to them.
Why it speaks of enemies
The prayer asks God to protect those who pray from every attack, so that they fear no enemy’s weapons. It is said after Communion in a Mass for peace that opens on the same hope. That first prayer asks for the peace the world cannot give, so that with the fear of enemies taken away the times may be calm under God’s protection. The Prayer Book kept it too, for evening prayer.
H. A. Wilson, The Gelasian Sacramentary (1894), book III, 56; William Bright, Ancient Collects (1864), the appendix
The Scripture in it
Now this is eternal life, that they may know You, the only true God, and Jesus Christ, Whom You have sent.
Bible text: Berean Standard Bible, public domain.
In Latin
Deus, auctor pacis et amator,
quem nosse vivere,
cui servire regnare est,
protege ab omnibus impugnationibus supplices tuos;
ut qui defensione tua fidimus,
nullius hostilitatis arma timeamus.
Per.
From H. A. Wilson’s 1894 edition of the Gelasian Sacramentary, among its prayers for peace.