is just meant as a Doctor Who inside joke, but it's actually very perceptive.
Ever read a poem by someone who thinks outside the box -- who is so above those stuffy, stodgy ideas like meter and rhyme that he can't be bothered to actually learn what meter and rhyme are for? And as a result, his poem stinks? To the arrogant outsider who doesn't understand what he's seeing, the "box" of meter and rhyme look small and constrictive; but once you get in there and make yourself at home -- man, there is all kinds of room.
Same goes for edgy, transgressive artists whose pieces are dull, dull, dull because, before they trashed the timeworn conventions of the past (things like perspective and composition), they never bothered to stop and figure out why those conventions were laboriously acquired and honed for so many centuries.
The same is true for the Faith. If you learn the combox version of Catholicism, it's just a long list of "thou shalt nots." What a small box! Who would want to climb inside there? Wouldn't you rather be freeeeee?
My little pea brain has made this argument to my soul over and over and over again. But every time I try to think (and act, and believe) outside the box, I discover that it’s actually smaller on the outside. And cramped. And dull.
Do you really want to be free? Make a vow. Be faithful. Take on a discipline. Say your prayers. Believe, so that you may understand. Think inside the box. It’s a lot bigger on the inside.