Athanasius wrote that the proof of Christ’s saving work “is clearer through visible facts than through arguments,” and proceeded to demonstrate it as follows (in De incarnatione 30 and 46):
For since the Savior works so many things among human beings, and daily in every place invisibly persuades such a great multitude, both from those who dwell in Greece and in the foreign lands, to turn to his faith and all to obey his teaching, would anyone still have doubt in their mind whether the resurrection has been accomplished by the Savior, and whether Christ is alive, or rather is himself the Life? Is it like a dead man to prick the minds of human beings so that they deny their father’s laws and revere the teaching of Christ? Or how, if he is not acting — for this is a property of one dead — does he stop those active and alive so that the adulterer no longer commits adultery, the murderer no longer murders, the unjust no longer grasps greedily, and the impious is henceforth pious?
When did human beings begin to abandon the worship of idols, except since the true God Word of God came among human beings? Or when have the oracles amongst the Greeks and everywhere ceased and become empty, except since the Savior revealed himself upon earth? … And when, in short, did the wisdom of the Greeks become foolish (1 Cor 1.18-24) except when the true Wisdom of God revealed itself upon earth? For formerly the whole inhabited world and every place were led astray by the worship of idols, and human beings regarded nothing else but idols as God. Now, however, throughout the whole inhabited world, human beings are deserting the superstition of idols, taking refuge in Christ, and worshipping him as God … And, what is amazing, is that while there were thousands of diverse objects of worship, and each place had its own idol, and that which was called a god by some had no power to pass over into the neighboring place to persuade those of the neighborhood to worship it … only Christ is worshipped by all as one and everywhere the same. And what the weakness of idols could not do — persuade even those dwelling nearby — this Christ has done, persuading not only those nearby, but simply the entire inhabited world, to worship the one and the same Lord, and through him God, his Father.
Aquinas picked up on this theme in Summa Contra Gentiles 1.1.6:
[The] wonderful conversion of the world to the Christian faith is so certain a sign of past miracles, that they need no further reiteration, since they appear evidently in their effects. It would be more wonderful than all other miracles, if without miraculous signs the world had been induced by simple and low-born men to believe truths so arduous, to do works so difficult, to hope for reward so high. And yet even in our times God ceases not through His saints to work miracles for the confirmation of the faith.
And Chesterton, finally, concluded his Everlasting Man along the same lines:
For this is the last proof of the miracle; that something so supernatural should have become so natural. I mean that anything so unique when seen from the outside should only seem universal when seen from the inside.
[…] The mystery is how anything so startling should have remained defiant and dogmatic and yet become perfectly normal and natural. I have admitted freely that, considering the incident in itself, a man who says he is God may be classed with a man who says he is glass. But the man who says he is glass is not a glazier making windows for all the world. He does not remain for after ages as a shining and crystalline figure, in whose light everything is as clear as crystal.
But this madness has remained sane. The madness has remained sane when everything else went mad. The madhouse has been a house to which, age after age, men are continually coming back as to a home. That is the riddle that remains; that anything so abrupt and abnormal should still be found a habitable and hospitable thing. I care not if the sceptic says it is a tall story; I cannot see how so toppling a tower could stand so long without foundation. Still less can I see how it could become, as it has become, the home of man.
[…] If it were an error, seems as if the error could it hardly have lasted a day. If it were a mere ecstasy, it would seem that such an ecstasy could not endure for an hour. It has endured for nearly two thousand years; and the world within it has been more lucid, more level-headed, more reasonable in its hopes, more healthy in it instincts, more humorous and cheerful in the face of fate and death, than all the world outside. For, it was the soul of Christendom that came forth from the incredible Christ, and the soul of it was common sense. Though we dared not look on His face we could look on His fruits; and by His fruits we should know Him. The fruits are solid the fruitfulness is much more than a metaphor, and nowhere in this sad world are boys happier in apple trees or men in more equal chorus singing as they tread the vine, than under the fixed flash of this instant and intolerant enlightenment, the lightning made eternal as the light.