This movie is basically a story about good vs evil, the evil being Woody Harrelson, who rules a small Texas town near the Mexican border with an iron fist. He is called 'Preacher' who is a combination of a mesmerizing, warped spiritualist with a Jim Jones-like influence over the townspeople, and a racist along the lines of David Duke, but much worse. The good is Liam Hemsworth, who plays a Texas Ranger sent by the governor to investigate the deaths of bodies (mostly Mexican) found dumped in the river that flows close to the town. Adding to the backstory, it's revealed that the Preacher killed his father when the Ranger was a boy.
The premise of the movie is implausible, and there is zero character development, making the movie somewhat of a Stepford Wives clone. But Woody Harrelson's portrayal of this Svengali/Mussolini monster propels the movie along nicely enough to keep you interested. Not much more can be said about it without spoiling the ending, which has a Quentin Tarantino-like quality to it.