"Here then we have two incredibles — to wit, the resurrection of our body to eternity, and that the world should believe so incredible a thing; and both these incredibles the same God predicted should come to pass before either had as yet occurred. We see that already one of the two has come to pass, for the world has believed what was incredible; why should we despair that the remaining one shall also come to pass, and that this which the world believed, though it was incredible, shall itself occur? For already that which was equally incredible has come to pass, in the world's believing an incredible thing. Both were incredible: the one we see accomplished, the other we believe shall be; for both were predicted in those same Scriptures by means of which the world believed. And the very manner in which the world's faith was won is found to be even more incredible, if we consider it. Men uninstructed in any branch of a liberal education, without any of the refinement of heathen learning, unskilled in grammar, not armed with dialectic, not adorned with rhetoric, but plain fishermen, and very few in number — these were the men whom Christ sent with the nets of faith to the sea of this world, and thus took out of every race so many fishes, and even the philosophers themselves, wonderful as they are rare. Let us add, if you please, or because you ought to be pleased, this third incredible thing to the two former. And now we have three incredibles, all of which have yet come to pass. It is incredible that Jesus Christ should have risen in the flesh and ascended with flesh into heaven; it is incredible that the world should have believed so incredible a thing; it is incredible that a very few men, of mean birth and the lowest rank, and no education, should have been able so effectually to persuade the world, and even its learned men, of so incredible a thing."—Augustine, The City of God (xxii.5)
But they did. Because the incredible gospel is incredible power.