My main takeaway from this movie is that the Devil needs to learn more patience.
Consider the facts: he's spent years setting up the perfect scenario to usher in the anti-christ. And early on in the movie, everything is going according to plan. He's got a solid hold on Lomax. Just keep feeding him headline cases -- you know, appealing to his vanity -- while he and his wife steadily grow apart. She shows little interest in adapting to life in NY and he shows little interest in slowing down for her sake. Give it a couple months, maybe a year or two tops, and she'd be back down in Florida with divorce papers in tote. That leaves Lomax open to pursue his attraction with the redhead. He doesn't even have to know she's his sister until much, much later. The only unease Lomax would experience is the occasional guilt pangs from getting criminals acquitted, which he's clearly already come to terms with.
It's perfect. Subtle. Devilish, even.
But NO. The Devil has to screw things up. Literally. He screws the wife, influences her suicide and asks Lomax to bang his own sister. Who wouldn't kill themselves after that?
So, Devil, a little advice: next time, have more patience. It's like that study with the kids and the marshmallows: don't grab the marshmallow right away. Wait the full three minutes and then get 2 marshmallows after the guy in the white coat comes back. Capiche?