Religion & Change

Q: Are religions always changing? To what extent are religions always changing and WHY do they change? Is the Christianity of today the same as the Christianity of 500 years ago-- or does religion change so much according to each age that in some respects it is a different religion?
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Though it seems that religion is forever changing and evolving with the rest of human culture, it seems to me that there are times when this process occurs very slowly and others when a combination of current events and the right leadership leads to rapid and far-reaching changes (the Diaspora and Reformation being only two examples that readily spring to mind).
I would have to agree that the Christian religion of 500 years ago differs in many significant ways from that which is most commonly practiced today. With a copy of the printed Bible available to virtually anyone interested in reading it, direct access to the accepted word of God is no longer solely in the hands of an elite clergy. Modern science has dispelled many of the long-held theories and superstitions to which our spiritual ancestors clung so dearly. Newspaper, radio, television and other media have bought the customs and beliefs of various foreign cultures within our grasp, bridging the gap between Christians and practitioners of other faiths long grouped under the collective label of heathen or pagan.
That said, I think the basic underlying truths beneath the metaphors attached to our various religions (and even denominations) remain basic and unchanged.
In order for the human mind to grasp the idea of an ultimate power or superior being, it is necessary to illustrate these things in a language we can all understand. As human society evolves, so too must our stories.