This objection also is cast in our teeth by Celsus: “From such signs and misinterpretations, and from proofs so mean, no one could prove him to be God, and the Son of God.” Now it was his duty to enumerate the alleged misinterpretations, and to prove them to be such, and to show by reasoning the meanness of the evidence, in order that the Christian, if any of his objections should seem to be plausible, might be able to answer and confute his arguments. What he said, however, regarding Jesus, did indeed come to pass, because He was a mighty potentate, although Celsus refuses to see that it so happened, notwithstanding that the clearest evidence proves it true of Jesus.
“For as the sun,” he says, “which enlightens all other objects, first makes himself visible, so ought the Son of God to have done.” We would say in reply, that so He did; for righteousness has arisen in His days, and there is abundance of peace, which took its commencement at His birth, God preparing the nations for His teaching, that they might be under one prince, the king of the Romans, and that it might not, owing to the want of union among the nations, caused by the existence of many kingdoms, be more difficult for the apostles of Jesus to accomplish the task enjoined upon them by their Master, when He said, “Go and teach all nations.”
Moreover it is certain that Jesus was born in the reign of Augustus, who, so to speak, fused together into one monarchy the many populations of the earth. Now the existence of many kingdoms would have been a hindrance to the spread of the doctrine of Jesus throughout the entire world; not only for the reasons mentioned, but also on account of the necessity of men everywhere engaging in war, and fighting on behalf of their native country, which was the case before the times of Augustus, and in periods still more remote, when necessity arose, as when the Peloponnesians and Athenians warred against each other, and other nations in like manner.
How, then, was it possible for the Gospel doctrine of peace, which does not permit men to take vengeance even upon enemies, to prevail throughout the world, unless at the advent of Jesus a milder spirit had been everywhere introduced into the conduct of things?
Source: Against Celsus (New Advent)