While the fiery destruction of the planet might sound like a downer (it's where I keep all my stuff!), this series is "apocalypse porn", appealing to the Nelson in us to enjoy a good "Ha-ha, you're going to Hell!"
Once upon a time, Christians got sick of being called hypocrites. Sure, the premise of their religion was love, peace, and compassion, but that shit is boring. For a long time, Christians got away with killing people, taking their stuff, and generally partying like they were Attila the Hun on crystal meth, but once the Bible got translated into a language the peasants could actually read, people started to ask annoying questions.
Annoying questioner: "Wait, what about this whole 'blessed are the poor' bit?"
Priest: "Because shut up, that's why."
So along came a guy named John Nelson Darby. His idea was that the omnipotent, omnicient god of the universe would obviously choose to communicate in secret codes, and that (properly decoded) this Bible code meant that all that stuff about peace and loving thy neighbor didn't apply to now (of course not!), it only applied to the perfect "Kingdom" that was going to exist after the end of the world. In addition to this, Real Christians™ would be safe from any unpleasantness associated with said end of the world because they would be "Raptured" away right before things got bad. Raptured people would get to sit in Heaven and watch with glee as all those unbelievers got what was coming to them. Obviously, this was more fun than all that loving kindness stuff, and wackaloons came from far and wide to join in.
Yup, those are the ones.
Fast forward to modern America. Angry at things like science and facts, the descendents of those wackaloons decided that nothing would be better than a series of books presenting their ideas to the world in fiction, because it was working so well for wizards and vampires, their ancestral enemies.
Not a Real Christian™
The plot is this: one day, all the Real Christians™ (no Catholics need apply) vanish. The world, predictably, heaves a sigh of relief and starts getting about the serious business of peace on earth, feeding and housing the world's poor, and getting on with things in a generally rational way now that the wackaloons are gone. A fictional counterpart to the UN starts making some real strides towards getting nations to stop fighting and generally stop being dicks. Sounds great, right? WRONG!
"It's a trap!"
Because in the world of Fundamentalist Christianity, world peace and cooperation are actually the goal of the evil forces of the ANTICHRIST!
"You will feed the hungry! You will stop killing each other! MUAHAHAHAH!"
Arrayed against the forces of peace and feeding the poor are the remaining Real Christians™. This is one of those places where you have to admire the realism of the series. But the Real Christians™ know they are up against something tin-foil hats just won't stop, so they recruit this guy.
Buck Williams: Action Hero
True to life, when faced with legislation they don't like, the Real Christians™ form a prayer group. And a militia.
More intimidating than the Tribulation Force
The Tribulation Force then does battle with the forces of global peace.
Not to scale
Unforgivably, the series does not end with Kirk Cameron getting slaughtered wholesale by the forces of darkness. Instead, the direct-to-DVD movies stop at the third installment, and we have to read another 13 books to find out (surprise surprise) the forces of evil and modernity are defeated and all the people who laughed at the ridiculous beliefs of the Real Christians™ end up tortured forever while gloating people in sweater-vests live eternally, glorying in the fact that despite all evidence and reason, they were right.