"No matter how religious one may be, one’s faith tends to change under unexpected and challenging circumstances."
When you say "one may be" it sounds too formal, you would refer to someone as "one" for a formal essay.
"No matter how religious you may be, your faith tends to change under unexpected and challenging circumstances."
Note: I changed "one’s faith" to "your faith" to make it sound less formal, fit for a more normal audience. Remember: you refer to someone as "one" if it is a formal essay or a college essay; for a more mature audience.