His one rhetorical move is "without this, Christianity collapses!" He is always, always talking about some fight that is so important, so crucial, so foundational, that it's vital to the Christian faith itself.
It's possible he thinks about and worries about all sorts of things that are important and yet not the life support of his faith, only blogging about the things that are this critical, but I suspect that, really, this is just his default. His one argument for everything he argues about.
If it's not the "the most central teachings of the Christian faith," it's "a non-negotiable of the Christian faith," or "it is not only the Bible that is subverted, but also the Gospel."
Etc., etc., etc.
Sometimes his claims about what's foundational make sense. He says, for example, that "The incarnation of the Word is the central truth of Christianity and the very foundation of our faith."
The incarnation has been interpreted different ways and understood in different ways, but every various permutation of Christianity can be rightly understood as a working out the belief in the reality of the incarnation. Whether, in practice, that looks like Liberation Theology or Jehovah's Witnesses going door-to-door, Pentecostal exorcisms in Brazil today, the East-West split of 1054 or the philioque debate. The Lollards preaching to peasants after dark or the Reformed Dutch masters painting cows. It has something to do with working out interpretations of the incarnation, because that's the core of what Christianity is.
Other times, it's really not clear at all how it's supposed to be so critical. He's doing the janga thing -- "don't pull that one: without that piece, the whole thing falls!" -- but it's just not clear why. Why, for example, is opposition to homosexuality the sine qua non of Christianity?
There are many many arguments that Christians should oppose homosexuality, of course. But I don't know of any that explain why this is essential to the faith itself, the rock on which it must be built so the gates of hell will not prevail against it.
Mohler, though, makes it sound like homosexuality is a more serious challenge than the Christian church has ever faced:
"The Christian church has faced no shortage of challenges in its 2,000-year history. But now it’s facing a challenge that is shaking its foundations: homosexuality."It's pretty funky history, if nothing else. I mean, there have been 39 anti-popes. There was a Thirty Years War. Mohler's own church was founded in a fight about slavery, and the side that said American slavery was Biblical and right came out of that quite successful.
Mohler doesn't circle back and give an explanation for why this is such a challenge, or a foundational issue. In general, he just asserts that the foundations are the foundations. And everything is foundation.
Maybe, ultimately, this just has to be read as functioning similarly to swearing: it intensifies whatever is being said, but you can't take it literally.