Faith as perception, not position
The most common mistake in writing religious characters is rendering their faith as a series of positions they hold rather than as a way of perceiving the world. A genuinely devout character does not only believe in God in the sense of accepting a proposition; they live inside a framework in which God is a constant presence — in the structure of the day, in the interpretation of events, in the conversation with the divine that runs beneath ordinary social life. Writing faith as perception means showing what the character sees rather than what they believe: the world as it appears from inside a living religious commitment, where meaning is distributed differently and significance attaches to different things than it does outside.