So much could have gone wrong. The rain could have poured on the crowd, someone could have slipped and fallen as they ascended to the altar, somebody could have fluffed their lines, or some idiot could have tried to spoil the day by streaking.
In the event, the crowd of 70,000 got a superbly choreographed and very traditional Catholic Mass. It was held in Glasgow's Bellahouston Park, nor far from the spot where the last Scottish Catholic martyr, St John Oglivie, met a hideous death, hanged, drawn and quartered in 1615 for denying King James was the true head of the English church.
One of the most impressive sights of the service was the stream of 450 white-robed priests marching down the steps and fanning out into the crowd to give communion.
As they descended the steps, the line seemed to be so long that it would never end, but the ratio was about one priest per 150 believers – meaning that they could have been swallowed in the crowd, except that someone had come up with the bright idea of ensuring that each of them was flanked by an attendant holding aloft a yellow umbrella.
Pope Benedict, as is well known, is a man who takes the ancient traditions of his Church seriously. It need not have come as a surprise to anyone that he conducted parts of his service in Latin. The BBC thought of that, and was ready with subtitles, but Sky, which was also broadcasting the service live, was caught unawares.
The concessions to popular entertainment came in the warm-up as the crowd waited for the pontiff and were treated to a performance by Susan Boyle, of Britain's Got Talent fame, and a Pop Idol named Michelle McManus. After the Pope had left, she stepped up again to entertain a much-diminished but cheering crowd with "Make Me a Channel of Your Peace".
SuBo may be a national treasure, but one of the greatest services that the organisers of the event did for their Church was to keep her out of sight during the service itself.
The only person to sing solo was a music teacher from Galloway, Laura Bohan, who led the congregation through Psalm 22 – "His goodness shall follow me always" whose voice was far superior to Boyle's.
The Pope's visit has stirred controversy, so he had a little dig at his critics during his homily, when he warned against what he called the "dictatorship of relativism" which, he said "threatens to obscure the unchanging truth about man's nature, his destiny and his ultimate good" and urged the faithful to speak out against "a jungle of self-destructive and arbitrary freedoms". It was more diplomatic than comparing Heathrow to a Third World country, but it was a reminder that this is a man with a mission.