In order for a religion to have staying power, and keep the interest of its members, it has to get involved in what is important to them. I.e. politics and war. You have to choose how you do this very carefully. Too aggressive, and you will attract too many enemies too quickly.
Religions that try to exist solely on RP find their members bored too quickly, and uninvolved. The rich, diverse religion is a labor of love of the founder, and no one else really cares.
You have to give your people something to do, and a goal for which to strive. That's how you get them involved. You do need the religious "window dressing", but it can be useful as a way to drive external conflict.
But no matter what, relate it back to what is important to your members: war and politics.
