A quotation from the first chapter of the Old Testament's Book of Ecclesiastes where the second verse reads,
Vanity of vanities, saith the Preacher, vanity of vanities; all is vanity.
The verse is generally taken to mean that man's activities on earth are largely futile.
We are reminded here of the title of Book 1 of Brideshead Revisited: the words Et in Arcadia Ego carry essentially the same message.
Listen to one man's memory of the bugle call to which these words were sung.
The relighting of the sanctuary lamp in the chapel at Brideshead symbolises the triumph of Catholicism in the face of loss of faith and sinfulness.
Not only has the faith been restored to members of the Flyte family, and experienced for the first time by Charles Ryder, but it is also a feature of the soldiers' lives while they are billeted at Brideshead Castle.
The restoration of the faith at Brideshead reminds Charles of the restoration of Christianity in Acre and Jerusalem during the First Crusade when the Crusaders defeated the Islamic occupiers of those Holy Land cities.
The reference to Jerusalem also reminds us that Cordelia now has no cause for the sadness she previously felt about the closure of the chapel - the sadness that she associated with the chant Quomodo sedet solas civitas (How doth the city sit solitary) which refers to the fall of Jerusalem in 586BC.