We must next glance at some natural causes which have been alleged as accounting for the wonderful spread of Christianity. Those brought forward by Gibbon in his _Decline and Fall of the Roman Empire_ (Chapter XV.) are five in number. The first is the _intense zeal_ of the early Christians. And doubtless this was a most important element in spreading their religion. But what gave them this intense zeal? What was it that made them so fearfully in earnest about their new religion, that they faced a life of suffering, and a death of martyrdom in preaching it? There can be but one answer. It was because they were so absolutely convinced of its truth. It was vouched for by what they considered overwhelming evidence, so they willingly risked everything for it. Their zeal, then, is but evidence for their conviction, and their conviction is but evidence for the truth of what they were convinced of; and valuable evidence too, for they plainly had much better means of knowing about it, than any that we can have. Secondly, there is the doctrine of a _future life_; and doubtless this also had much to do with the success of Christianity. A longing for immortality seems inherent in man, and the vague guesses of philosophers were quite unable to satisfy this. It _might_ be true that men should live again, but that was all they could say. Christianity alone, resting on the actual fact of Christ's Resurrection, said it _was_ true; so here men found the assurance they wanted. But is it likely that Christianity should have so thoroughly satisfied them in this respect, had there been any real doubt as to Christ's Resurrection? Thirdly, we have the _miracles_ ascribed to the early Christians. Gibbon's argument here is more difficult to follow. Of course if these miracles were true, they would have greatly assisted the new religion; but then they would have been, not a natural but a supernatural cause of success. If on the other hand, the miracles were false, it is hard to see how the early Christians could have helped their religion by claiming miraculous powers which they did not possess, and which their contemporaries must have known that they did not possess. Fourthly, we have the _pure morality_ taught and practised by the early Christians. And no doubt this had something to do with helping their religion. But again we must ask, what was it that enabled the Christians alone in that age of vice and wickedness to lead pure lives? They ascribed it themselves to the example and power of their Founder, and nothing else can account for it. Christian morality cannot be a stream without a source, and no other source can be assigned to it. But could a mere human Teacher have had this more than human influence over thousands of converts, most of whom had never seen him?