These days, rather few practicing Christians are actually expecting to come face to face with Jesus Christ in this life, on this world. Sure, some Bible Belt revivalists will preach that "The end times, they are a'comin!", and, sure, some of the more dysfunctional, mentally disabled Christians may really believe that Jesus is about to reveal himself. Nevertheless, given the fact that it's been over 2,000 years now, and this hasn't happened, most Christians do not expect the Book of Revelation to be actualized and made real for them, for their children, or for their children's children. One cannot readily imagine the Pope, the leader of one billion relatively organized and centrally controlled Catholics, announcing that his flock must prepare for the imminent arrival of Jesus, and the end of the world. He'd probably have to retire at that point, if he did.
However, in the early days of Christianity, the Book of Revelation was taken very seriously, indeed. Saint Paul of Tarsus most certainly believed in it quite literally, and believed that Jesus could come back any time, and almost certainly sooner rather than later. And, in fact, arguably, this was actually the main selling point of Christianity, for early Christians. This really cool guy, Jesus, who could perform miracles, and rose from the dead according to numerous eye-witnesses, was actually God himself, and was about to return, to claim the world as his own, and to make those who followed him Princes with eternal life. What a deal! What other religion could make an offer like that? None!
Now, naturally, as the centuries passed, and Jesus did not return, this offer began to pale a bit. After all, if Jesus was not about to return, what did Christianity really have to offer people? Misery and self-denial in this life, and the unproven and unprovable prospect of some vague reward in a hypothetical after-life. Not really that great a deal, at all! And, it was at this point that Constantine the Great made a deal with the early Christians -- Christianity would be made the state religion of the world's greatest empire, the Empire of Rome. Thus, some of the ideals of Christianity would be integrated into the structure of the State on earth, and, hence, the nature of Jesus could, perhaps, be to some extent infused into life on earth, prior to Jesus' actual return. Not quite a good as Revelation, of course, but, still, perhaps something of an improvement, and a reasonable rationale both for the continuance of Christianity as a religion, and the continuance of the Roman State as an Empire. And, although the Western Roman Empire did not long survive, the Eastern Roman Empire lasted another thousand years, propped up by the ideals of Christianity. And the Roman Catholic Religion has survived as a kind of State within the State, till the present day.
You see, even transcendental religions like Christianity, and Buddhism, religions focused on the "after-life", really do have to appeal to people in this life. In the case of Christianity, it was the original belief in the imminent second coming of Christ, and, subsequently, the existence of the alternative "Christian State", the Catholic Church. In the case of Buddhism, the appeal is the absolute certainty that Buddhists have that they will be reincarnated after death. How can they be so certain, you ask? Well, it's been proven, of course! In the laboratory. Scientists in Buddhist countries consistently find overwhelming proof of the existence of "hidden memories" from past lives in almost everyone. And, these proofs are overwhelming. As good, or better, than our Western scientists' proofs of Einstein's Theory of Relativity, for example. So, Buddhists have every practical reason to worship the Buddha and his views, in expectation of a better life in their next reincarnation. Eminently practical, don't you think?
Now, given the failure of Jesus to return, and the collapse of the Western Roman Empire, it's not surprising that alternatives to Christianity began to develop, and Islam is the prime example, largely a reaction to the failures of Christianity. Islam is NOT a transcendental religion. Islam is an eminently pragmatic religion, of the present life. Islam is "instant government", for those living in primitive anarchy. Law, morality, religion, the state, life and culture are combined into one elegant whole. And, as we can see even now, in Saudi Arabia, Iran and Afghanistan, Islam has great power to resist even the predations of the greatest powers on the planet, when pursued with true fervor and intensity. Muhammad really knew what he was doing, didn't he?
So, what if the second coming of Christ hadn't been a fundamental tenet of early Christianity? Christianity never really takes off, it has no particular appeal. The Roman Empire falls earlier, and more completely. Islam never develops, at all. The only organized religious Empire is Chinese Buddhism, and we're all Chinese speaking Sino-Confucian-Buddhists by this time. Thoughts?