He tries to out-pope the Pope by following every rule strictly.
outpope the Pope
idiomTo act as a more authentic member of a group than one who is actually a member of the group.
The new employee is so eager to impress that he tries to out-pope the Pope by arriving an hour early every single day.
In his desperate attempt to gain favor with the traditionalists, the convert often out-popes the Pope, displaying a level of zeal that even the most devout members find excessive.