Now what was the cause of this wonderful progress? It is easy to say what was _not_ its cause. Physical force and the authority of the Government had nothing to do with it. Its missionaries did not preach with sword in hand, nor were they backed up by the civil power. All they did, all they could do, was to appeal to man's reason and conscience, and this appeal was successful. And we learn from the Christians' themselves, _e.g._, in the Acts, that there were two main reasons for this. The first was the confident appeal to the facts of Christianity, such as the Resurrection of Christ, as undisputed and indisputable; and the second was the occasional aid of miracles. And the more we reflect on the subject, the more difficult it is to account for it, without at least one of these causes. For the spread of Christianity was not like that of a mere philosophy, or system of morals. It depended entirely on certain alleged _matters of fact_, which facts were quite recent at the time of its origin, occurred at the very place where it was first preached, and were open to the hostile criticism of an entire nation. This, it is needless to say, is without a parallel in history. But it may be said, notwithstanding this rapid progress at first, Christianity took nearly three centuries to conquer the civilised world. Undoubtedly it did, but the significance of the conquest is not diminished by this. It is rather increased when we remember that at intervals all through this period the Religion suffered the fiercest persecution. That it should have survived such a fearfully prolonged struggle, and have finally conquered, does but show its inherent strength. We may look in vain for anything like this in the rest of history. No other religion has ever withstood such persistent attacks; no other religion has ever obtained such a complete and almost incredible triumph, the Emperor of the civilised world being brought to worship One Who had been put to death as a malefactor. In short, the progress of Christianity was as unique as its origin, and can only be satisfactorily accounted for by its truth. (3.) _The so-called natural causes of success._