So what is faith, anyway? There are several aspects, but luckily I have several characters (grin) to explore some of those facets with. The shattered faith of the disillusioned. The emptiness of having no faith at all. And at the other end, the bitter anger toward an unjust god. In every case there is a reason why the person arrived there. In each instance, there is a genuine opportunity for rediscovery.
For me, and for these characters, finding faith, and personifying such faith in a god, is all about the journey and not the resolution. The worn phrase "God is all around you" takes on new meaning when you see a divine hand in what's taking place rather than being dunked in a pond. A soul's search for meaning in their lives may not even start with a religious intent. How faith is restored, be it in the discovery of self, others, or an over-arching deity, is the real story for me.
So lets talk about that trio I mentioned at the start. The Saint finds that the church titling her is a sham. The musician was so wrapped up in his own struggles that when he finally frees himself, he has...nothing. The alien rejects her gods, hating them for the infliction visited on her people. These deep issues simmer in the background, but they guide both the characters and the story along the journey. As a writer, I cannot afford to lean on a lectern and preach toward any given religion we have today. Great way to lose readers. What I will do, however, is study this powerful undercurrent in our society called "faith". There was a line out of a favorite SF movie of mine ("Serenity") where a preacher implores the main character that it wasn't important what he believed in, just that he believed. Powerful stuff when you dwell on it a tad.
A writer would be wise, in my opinion, not to foster a new religion (that's happened before with disastrous results) or force-feed an existing one. There's no middle ground for the hapless author as they will be assailed by believers and non-believers alike. Especially these days. Running through a shooting gallery would be preferable, and many writers simply drop faith of any kind from their stories altogether. That's too bad. Love, hatred, and survival tend to be the prime motivators for stories, but what about belief? Faith is so powerful that it can transcend all three of those previous categories. The trick is to understand that there are many types of faith springing from multiple sources. One doesn't have to settle on a religion. Or hide from one.