My wife and I did this. We were both raised Jewish but honestly, aren't religious at all, and so we were worried that if their position was to let "Jesus take the wheel" so to speak, that it wouldn't be for us. It was not. Honestly, I didn't feel as though religion had much of anything to do with the program itself.
I don't like to say too much about the program because it's one of those things that is honestly better if you go in "blind". I will say however that the program helped us to learn to communicate better, and gave us tools to help us understand ourselves and our partners more, and in infidelity, that's important. There were couples there that walked in the door unable to even look at each other without starting a fight, and by the end, most people felt calmer and more connected and understood.
A few things:
You will never HAVE to speak in front of others or share if you don't want to, so don't worry. Sharing is optional.
There are opportunities to meet and talk with other couples if you like, however you will never be interacting with them as part of the course. In other words, you will only be working with your spouse, not some other couple or their issues.
The days are long and packed. You will go to bed at night and be asleep by the time your head hits the pillow. Don't make plans to see the town while you are there. There won't be time.
The program is designed to avoid conflict especially early on. Everything is voluntary. You will be given safe topics to work with. At no point will be you forced to do anything you don't want to. It takes no special skills or talents. They provide everything you will need except they do ask for pot-luck snacks and drinks, which is great because you bring whatever you like and then at least you know there will be a snack you enjoy.
If you are the type who wants to be more involved, you can be, and they are happy to tell you about being part of the program, or joining group events (such as a holiday party). But these are 100% optional.
I don't think this program will fix all your problems, so don't go in with that hope. Rather, this is another tool in your toolbox, and a way to hopefully open a path to better communication between partners when none seems to exist.