One of the more interesting things to me is that this particular delicacy was mainly used by Muslims through the Middle Ages:
At one time coffee was consumed by Oromos and Muslims only. The clergy condemned the use of coffee. However, at a later date coffe won the palates and hearts of even the strictest of the priesthood.
Coffee did not become an intrinsic part of Ethiopian culture until the 1880s when Menelik [II, Emperor of Ethiopia from 1889 to 1913] himself drank it. At that time the Egyptian Bishop of the Ethiopian Orthodox Church, Abune Matewos [bishop from 1881 to 1926], dismissed the clergy's contention that it was a Muslim drink.
(Daniel J. Mesfin, Exotic Ethiopian Cooking [Falls Church, VA: Ethiopian Cookbook Enterprises, 1993], p. xxvii.)Abune Matewos, was born and educated in Egypt. He may not have understood the local Ethiopian Christian aversion to coffee; he certainly did not share it.
Why was coffee a Muslim drink. One of the main reasons was that coffee did not contain alcohol (like beer or wine) and so you could not get drunk from it, it required boiling so it killed the germs in the water, and it had its own chemicals with neurological side effects.
So coffee has always been prohibited by some Christian sect or other throughout its entire history.