John Olav Hodne, a parish priest at Melhus Church, just outside Trondheim, failed to notice anyone moving around in the room during the service, even though its entrance stands just a few metres from the alter.
"I didn't see anyone," he told The Local. "During the service, someone came into the changing room for the vicars and took this case with my phone and my credit cards."
"It is a particularly disagreeable and unusual theft," Ebbe Kimo from the South Trøndelag Police told Norway's NRK. "We hope that the matter gets a little attention so we can get some tips. It could be that someone saw something suspicious around Melhus church this morning."
When The Local first contacted Hodne on Monday, he was unaware that the theft had made national news in Norway, and went so far as to ask whether he was being called by the thief.
"Do you have my phone and my credit cards and everything?" he asked suspiciously.
Later, he argued that stealing from a church was no different from stealing from a house. "It's terrible anywhere," he said. "The most annoying thing is all the work it costs to close up your cards and close up your sim cards, and on top that I've had so many journalists calling me, and that's a whole lot of work too."
Reidulf Krossli Ljøkjell, who was pastor of the same church up until 2009, told Aftenposten that he had also had his mobile phone stolen during a service.
"I think I saw someone moving around back there at the time, but you can not do much while you're leading worship," he said.
"You also have to get pretty close to the priest holding a church service when you go in there," he added. "It's a bit cheeky."