They're most likely going to renew their wedding vows. It's fairly common.

A lot of couples around here "re-take" their vows after 10 or 20 years - it's like a reminder of why they married in the first place and/or of the promises they made to each other way back when.

I've only heard of a couple people that actually went through the whole marriage process again rather than just the vows, but hey, it must have meaning for them.

-Nikira

I'm not much one for weddings and religious ceremonies and stuff, but some people have a BLAST doing it.

I suppose it's like if you were only supposed to celebrate Halloween once. I'd have to re-do it at some point.

This is actually a good thing. This means they really like each other very much.

But on the subject of you not knowing much culture etiquette besides removing hats!

It's also sometimes proper to remove your jacket!