THE THING IN THE WOODS, The Workers in the Vineyard, and the Cost of Discipleship
Although I don't buy the idea that all art "has a message" or "all art is political," odds are the longer one's book or the deeper its ideas, the more likely it's going to touch on something pertaining to politics, culture, spirituality, morality, etc. even by accident. And art very often reflects its historical-cultural context and the values of its creator. Since I am a Christian, my horror novel The Thing in the Woods does reflect that, in particular the journey of the character Sam Dixon.
The following discussion contains spoilers for Thing, so be ye warned...
Sam, one of the four (human) point of view characters in the book, is a middle-aged veteran of the Persian Gulf War and a member of a cult that has been worshiping an alien horror in the woods outside the small Georgia town of Edington for several centuries. Early in the novel, he begins to question the cult for its murder of a homeless veteran. Later on, he begins to suspect the thing in the woods is not actually a god (after all, an "unethical" deity is still a deity and disobedience will likely have unpleasant consequences, but something lacking in demonstrable supernatural powers might not be), undermining his faith still further. The final straw is when the cult leader sends his enforcer Reed after Sam (ostensibly just to beat him severely rather than kill him), but Reed exceeds his orders, beating Sam's wife and nearly killing Sam himself before another character intervenes. Not long after, Sam explicitly renounces the worship of the monster in the woods and vows to serve "the real Lord."
Sam's story is explicitly based on Jesus' Parable of the Workers in the Vineyard, in which a generous landowner pays day laborers a full day's pay whether they worked a full day or only a short time. Per my college pastor, if you were a hired laborer in Roman Judea, if you didn't work a particular day, you didn't eat that day. From a salvation point of view, someone who becomes a Christian later in life is just as "saved" as someone who has served the Lord from childhood. Although many critics of Christianity object to the idea that one can repent of a lifetime of horrible behavior (including theoretically Hitler--the movie Fury features a discussion on this) and still be saved, someone who intends to sin until the last minute and then "repent" and be forgiven is clearly not remorseful and thus isn't really "saved." A person who is aware of this particular doctrine and believes that God will decide their fate in the hereafter clearly believes in God, but he isn't obeying him. As the Apostle James pointed out, even Satan believes in God.
Furthermore, as James put it, true faith produces works. The man who would become Saint Francis of Assisi abandoned his hedonistic lifestyle and crass materialism to become a begging friar, the murderous WWII governor-general of German-occupied Poland Hans Frank voluntarily turned over extensive documentation of the Nazis' crimes that was then used to convict and hang him, serial killer David Berkowitz refused to seek parole for many years (to the point of skipping mandatory parole hearings), admitted he deserved his life sentence, and wanted monies made off him by lawyers and others donated to his victims' families, and the infamous "General Butt Naked" of Liberia testified before the country's war-crimes tribunal and is now a preacher who raises money to rehabilitate child soldiers.
(A more secular example of this is the 1998 American Godzilla film in which the reporter Audrey steals military secrets from her still-infatuated ex for what she hoped would be the scoop of a lifetime, causing him to lose his job. She--and her wacky ethnic comic relief cameraman who along with his wife had encouraged her in her misdeed--follow him into Godzilla's lair and ultimately plays a pivotal role in preventing a mass breakout of Godzilla's offspring that could destroy human civilization. Given how pretty much everybody involved knew the risks, most of them ultimately ended up lizard lunch, and it was Audrey herself who broadcast the "kill us to save humanity" message, "prove your repentance by your deeds" indeed.)
And although American Christianity doesn't emphasize this to the degree it should (*cough* prosperity gospel *cough*), following Jesus has a cost. German theologian Dietrich Bonhoeffer, who wrote The Cost of Discipleship on this very topic, ultimately died in a concentration camp for his involvement in the German resistance against Hitler. In Thing, Sam assists protagonist James Daly and his not-yet-girlfriend Amber Webb in infiltrating the cult's compound to rescue James' abducted father where, to make a long story short, he ends up getting eaten alive by the monstrosity he'd spent most of his life worshiping. His repentance, although it meant he would go to Heaven rather than Hell, ultimately cost him his life.