Op/Ed in the Wall Street Journal goes over the history of how the Court can review law. Not as dry as you might think, when you consider the current cases (my emphasis)
What is made clear, over and over again, from leaders of the anti-gay marriage movement ranging from Speaker of the House John Boehner to the so-called National Organization for Marriage is that their positions are based on religious belief and a particular interpretation of the Christian Bible. Boehner had spoken of never changing his position on the matter because that is what his church tells him it should be. In the opening sentence of their mission statement the NOM states that they have: "a mission to protect marriage and the faith communities that sustain it [emphasis added]." Their leader, Brian Brown, talks about how his position is drawn from "Scripture" and "biblical views of marriage" .
Of course any church is entitled to formulate and abide by its own rules for marriage, and if they don't want to countenance or recognize same-sex marriage, under the First Amendment they love to denigrate so much, that is their right. But then there is the institution of marriage (with provisions for its legal dissolution) that is found in the civil law that exists on the books of every one of the 50 states. This institution has absolutely nothing to do with religion any more than state motor vehicle laws do. In every state a couple can walk into the office of an civil official endowed by that state's law to perform a marriage ceremony and certify that it is licensable under the law, and get married. Unless, that is, in most states, they happen to be of the same sex.
And so, there are only two issues that should be considered here. Both are Constitutional. The first is whether, given the "no religious establishment" clause of the First Amendment, a definition of marriage that is clearly based on religious belief, according to its proponents, should, indeed can, be granted any recognition under the law at all (other than to protect its use for religious weddings by those who hold to that religious belief under the "free exercise" provision of the First). The second is, given the fact that each of the 50 states has a large body of civil law concerning marriage, whether or not the "equal protection" clause of the 14th Amendment applies.
We are talking about religious determination of civil law and practice here. ... When the issue is before the Supreme Court it is the defense of the Constitution, of the 1st and 14th Amendments, that should be at the center of our side's arguments, and nothing else.