Ethan Hunt (Tom Cruise) has to infiltrate Vatican City to attend the same party as arms dealer Owen Davian (Philip Seymour Hoffman). So what does he do? He scales the side of the wall, before abseiling down the other side and quickly donning a disguise as a priest.
It's a fun, quick stunt that leans into the silliness of the franchise, while still looking cool. But it's far from the biggest sequence of the franchise.