If you’re a Christian, it shouldn’t be a secret.
Some people keep their religion under wraps. Sometimes ’cause they’re afraid of backlash—“You’re a Christian? Well, I’m an atheist. How can you believe that crap?”—or “persecution,” which is what far too many Christians tend to call backlash. (Real persecution is illegal in the United States, you know.) Much of that fear is irrational, but it’s there.
Sometimes it’s because they don’t wanna be known as a Christian. They want to behave like pagans, and not have any of their friends turn round and say, “I thought you were Christian. How can you behave like that?” (’Cause there’s nothing more annoying than pagans rebuking your bad behavior. Sad to say, I know this from experience.) That’s a hypocrisy thing, and I hope that’s not your hangup.
And sometimes it’s because they honestly don’t know how to announce their Christianity to the world.