@sometime sun,
I think the function of church has adapted to the era of it's existence. It meets the need of society. If I were to guess, I would say the most primitive churches were purely and spiritually religious.
Flashforward to the Jihads, and any eminent Imam(I may be wrong) could sanction a Holy War. The mosque, or masjid or something, commanded power. It assured solidarity among muslims, therefore strengthening its own religious agenda.(Here I am naively purporting that the Koran beckons violence or protelyzation against infidels:/)
Hundreds of years down the road, the Pope could approve a crusade and carry out his or "god's" will. The church ensured security in turbulent times, because society NEEDED it. The church facilitated control of the overwhelming number of people it needed to suppress.(Redundant i know) Those were the dark ages.(My chronology is terrible, sorry)
American independence further shaped the function of the church. The church could not as ably fit the form of a society founded on the righteousness of your own person. The church grew smaller.(Incrementally)
World War 2 made America the most powerful nation on earth. There was little a church can offer in terms of security in post-war America. The church grew smaller.
Today, though Americans live under the banner of one nation under god, church membership is drastically low. Why? Some say the moral decay of TRUE american values.(Or at least conservative republicans) I believe the reason is there is little want for it. Plus those pews are so damned uncomfortable. Why do we see so many cell phones? Because the need for them is high. Because we are/were wealthy nation. And becaues i want a flipping cell phone! There is no longer much a church can offer. In an age of narcissism and commercialism(im generalizing) The church is being edged out as the Walmarts of America become almost religious sanctuaries.
Bereft of any data, pie charts, or line graphs,(and because I am an haughty self righteous American!) I will near groundlessly relate the facility of church to the only functions it can now perform: religion, community, weddings, funerals, and charity. And this is not to say the church monopolizes these concepts, but it is all it has to offer. Sooooo, nothing I would personally say, unless i can be contradicted, that the church offers almost nothing besides free parking and weathervanes.