The Senators and Representatives before mentioned, and the Members of the several State Legislatures, and all executive and judicial Officers, both of the United States and of the several States, shall be bound by Oath or Affirmation, to support this Constitution; but no religious test shall ever be required as a qualification to any office or public trust under the United States.
I think it's important to be clear that we're about to see the principle of a religious test reinstated in the United States, depending on how the Supreme Court rules on gay "marriage".
There are approximately 70 million Catholics in the United States of America, or just under 1/4 of the country's population. The official teaching of the Catholic Church on the subject of gay "marriage" is this: while homosexual attraction is not sinful, acting on that attraction is sinful, and marriage remains the union of one man and one woman. In other words, gay "marriage" is something Catholics can't believe in, advocate for, or approve of while remaining Catholics in good standing with the Church. Granted, lots of those 70 million Catholics are non-practicing and functional heretics anyway, but the point is that you can't in any way claim that the Catholic Church approves of gay "marriage," because she doesn't, and won't ever do so.
However, if SCOTUS decides to "Roe" the nation on gay "marriage" and impose it on the nation via judicial fiat, one of the most immediate effects of such a ruling would be to require a de facto religious test for many public offices. Because the ramifications of a SCOTUS pro-gay "marriage" ruling would be to define those who don't accept gay "marriage" as bigots and any anti-gay "marriage" position as bigotry, the Supreme Court would essentially open the door for a prohibition against "bigots" holding many public offices. This would mean that the only Catholics who would qualify for public office would be the heretical ones who dissent against Church teaching against gay "marriage," while faithful Catholics who accept all Church teaching would be barred--officially or unofficially--from serving in many branches of the government. An immediate example that comes to mind is that of chaplains serving in the United States Armed Forces: will they be required to officiate at gay "weddings" or to otherwise violate Church teaching, or will the government simply decide that "bigots" don't get chaplains anymore? I fully expect that to be one of the early battlegrounds.
If the Supreme Court decides that opposition to homosexual acts and opposing the pretense of two-man or two-women "marriage" is the same thing as racism, then no quarter will be given to any religious citizen whose deeply held religious beliefs oppose gay "marriage." Whatever is done to Catholics and the Catholic Church in a post-gay "marriage" America will be the template for the eradication of religious beliefs that call homosexual activity sinful on the grounds that to hold such beliefs makes one an evil bigot who cannot be tolerated by a free secular people.
The religious test is coming. Are we ready?