In your opinion what causes christians to believe in Jesus

[Alan V]

Of course people have faith in God without knowing he exists.  Perhaps you meant something else by that.

You personally might not be convinced he exists, but clearly others are. And even if you're right and they're wrong, the point still stands: Faith is not the means by which that belief comes about. You have to already believe in his existence before you can have faith.

Then what you meant was "You have to believe he exists before you can have faith in him," not "He has to exist before you can have faith in him."