"Selectively Abid[ing] by Biblical Teachings"

That's not for secular courts to judge.

A commenter on the videographer / same-sex wedding thread writes,

So the Larsons won't shoot weddings if the couples had premarital sex because that would "promote sexual immorality"?

Or do the Larsons selectively abide by biblical teachings when it suites their personal morality and political leanings?

My guess is that the Larsons don't care about past sin, but about things they view as celebration of sin. They thus likely would shoot weddings if the couples had premarital sex—or if they had had same-sex relations in the past, for instance with other partners or in a threesome—but wouldn't shoot ceremonies that affirmatively celebrate premarital sex (e.g., a "shacking up" ceremony, if such a thing exists).

But from the perspective of American First Amendment law, all that is beside the point, because it isn't for courts to decide whether people are unduly "selectively abid[ing] by biblical teachings." Religious people often have to decide what biblical teachings mean, which ones have special significance, and which ones also impose a duty on third parties not to be complicit in various ways with certain conduct (as opposed to not just requiring that conduct). Indeed, since almost all Christians (1) view the Old Testament as very important, but (2) don't comply with all the rules of the Old Testament (such as the kosher laws), they necessarily have to decide which "biblical teachings" remain obligatory and which aren't. And though some religious observers may make that decision based on what they see as purely theological considerations, others will consider their "personal morality" to the extent that it is itself informed by their understanding of their religious obligations. None of that limits either their Free Speech Clause rights or their Free Exercise Clause rights.

Don't just listen to me on this, though; consider the 8-to-1 decision in Thomas v. Review Bd. (1981) (Justice Rehnquist dissented on other grounds), which involved the Free Exercise Clause precedents that generally required unemployment compensation to be paid to people who quit their jobs because of felt religious obligation. Thomas had quit work because he was transferred to a department that made materials for military weapons. The state rejected his Free Exercise Clause claim:

The Indiana Supreme Court … concluded that "although the claimant's reasons for quitting were described as religious, it was unclear what his belief was, and what the religious basis of his belief was." In that court's view, Thomas had made a merely "personal philosophical choice rather than a religious choice."

In reaching its conclusion, the Indiana court … [noted] that Thomas admitted before the referee that he would not object to "working for United States Steel or Inland Steel … produc[ing] the raw product necessary for the production of any kind of tank … [because I] would not be a direct party to whoever they shipped it to [and] would not be … chargeable in … conscience …"

The court found this position inconsistent with Thomas' stated opposition to participation in the production of armaments.

But the U.S. Supreme Court disagreed:

Thomas' statements reveal no more than that he found work in the roll foundry sufficiently insulated from producing weapons of war. We see, therefore, that Thomas drew a line, and it is not for us to say that the line he drew was an unreasonable one….

The Indiana court also appears to have given significant weight to the fact that another Jehovah's Witness had no scruples about working on tank turrets; for that other Witness, at least, such work was "scripturally" acceptable. Intrafaith differences of that kind are not uncommon among followers of a particular creed, and the judicial process is singularly ill equipped to resolve such differences in relation to the Religion Clauses.

Naturally, all of us are free to second-guess others' interpretations of scripture in coming to our own evaluations of the morality or reasonableness of those others' behavior. But American secular courts cannot make decisions based on such an analysis, or decide that someone's beliefs really are consistent with the Bible and someone else's aren't.