The problem with that, though, is that Christianity (or pretty much any present-day religion, for that matter) didn't invent "marriage", concept or otherwise.
"Marriage", as a concept, has existed far longer than most current day religions, including Christianity, so it's not something that belongs strictly to your religion, or mine, or anyone else's.
Nor is it something that we can say "can't and/or shouldn't be redefined", because we ourselves didn't "define" it in the first place, nor did we "make" or "invent" it.
Obviously I'm not trying to make you support it if you don't, but it wasn't really "redefining" if your religion didn't make it in the first place.
We didn't invent the concept of "marriage", so we can't "define" it, regardless if it's been a certain way for a long time or not.
Also, like I said before, though I definitely support the ruling, I don't think churches or any religious figures should be forced to marry anyone that they would otherwise refuse to, regardless of the reasoning, with this being no exception.
If the church and/or religious person in question are perfectly okay with doing it, then great!
But if not, then they shouldn't be forced to do something they don't want to whatsoever.
You can get married outside of a church anyways, so it doesn't really matter.
That's just my thoughts, at least. *shrug*