Well I have to argue that mercy and justice do co-exist. I found this on the internet, which is becoming the encyclopedic wizard of the world's knowledge.
In his justice, God judges us because we are guilty. Then in his mercy and love he comes down in the person of his Son, Jesus Christ, and pays the penalty for us. Through the sacrifice of Jesus on the cross, God is both just and merciful.
So in other words, Jesus died the death we deserve so we can live the life He deserves. I am a Christian and believe this. But I respect the beliefs of others and don't condemn those who believe differently.
Religion is a tricky subject, like I mentioned before. People have definite ideas about what they believe. But I see a trend in the past few years of declining church attendance and membership. I could go into the reasoning behind this, but this is not the forum or platform for that.
So in my mind, if you put religion in a story, it better be believable and relevant. Do your research.
It might be interesting to work a story around The Amish, but there are romance novels out with that genre. What about Quakers? The Shakers? How about a cult, similar to Jim Jones of kool aid drinking fame in Guyana? There is a cult in Montana that is pretty weird, try to make up better stuff than the stories about the Church Universal and Triumphant. (Sorry if I offend any members of that group that might be on this site.) I can let you know a few, I used to live down the road from them.
So, make it believable! Make me want to leave my church and join yours! Make that preacher charismatic! Watch the religious channels on DirecTV. Wow us.
Queen Norma Jean