The decision means eight major religious groups in the US now support same-sex marriages. Here's a chart showing which are supportive, opposed, and unclear, from the Pew Research Center:
This is a slightly different chart from the one posted by Pew early last year. Back then, both the Episcopal Church and Presbyterian Church (USA) supported same-sex unions, but not marriages. They've officially shifted over to the lefthand column now.
Now, a church's official position doesn't necessarily reflect the opinion of its members. A massive survey of Americans from the Public Religion Research Institute found 60 percent of Catholics support marriage equality, even though the Vatican doesn't. And 84 percent of Buddhists supported same-sex marriage — the highest levels of support — even though their position is unclear in official doctrine.
But the acceptance of same-sex marriage by institutions matters, since it signals that marriage equality is turning into an issue that religious leaders aren't willing to fight anymore. So as more churches shift to support same-sex marriage, you can tell that LGBTQ advocates are winning.