<<Marriage is purely religious.>>
I suppose that's true in Islamic states that are governed by Sharia law. Obviously, and thankfully, it's not true in the United States, where we enjoy freedom of religion rooted precisely in the separation of church and state. 
<<The Supreme Court does not have authority over marriage.>>
But it does. Faith communities can define marriage for their co-religionists, but not for others. Secular marriage is a civil contract which creates rights and duties under civil law. The legislatures and courts have jurisdiction only over the secular contract; they neither have nor claim to have authority over religious definitions.
People of faith can advocate their understanding of marriage in the public square, but they have no privileged place in the debate. Moreover, many persons of faith -- most, I think -- support the Court's decision.  I'm a Catholic. Most of my family and many of my friends are Catholic. None of them thinks the Court got this wrong.