Their goal, until recently, was to perpetuate their numbers and grow. You can consider it the equivalent of a nation state conquering other nations or a corporation buying other businesses in order to 'grow'. In one word, expansion.
Power over others yes, but what I mentioned is a form of power.
They offer nothing of any value to humanity. At least the Catholic and Adventist churches run hospitals and other charities.
Now wealth has been added to the equation.