I do not understand how Celsus should deem it of advantage, in writing a treatise against us, to adopt an opinion which requires at least much plausible reasoning to make it appear, as far as he can do so, that “the course of mortal things is the same from beginning to end, and that the same things must always, according to the appointed cycles, recur in the past, present, and future.” Now, if this be true, our free-will is annihilated. For if, in the revolution of mortal things, the same events must perpetually occur in the past, present, and future, according to the appointed cycles, it is clear that, of necessity, Socrates will always be a philosopher, and be condemned for introducing strange gods and for corrupting the youth.
And Anytus and Melitus must always be his accusers, and the council of the Areopagus must ever condemn him to death by hemlock. And in the same way, according to the appointed cycles, Phalaris must always play the tyrant, and Alexander of Pheræ commit the same acts of cruelty, and those condemned to the bull of Phalaris continually pour forth their wailings from it. But if these things be granted, I do not see how our free-will can be preserved, or how praise or blame can be administered with propriety.
We may say further to Celsus, in answer to such a view, that “if the course of moral things be always the same from beginning to end, and if, according to the appointed cycles, the same events must always occur in the past, present, and future,” then, according to the appointed cycles, Moses must again come forth from Egypt with the Jewish people, and Jesus again come to dwell in human life, and perform the same actions which (according to this view) he has done not once, but countless times, as the periods have revolved. Nay, Christians too will be the same in the appointed cycles; and Celsus will again write this treatise of his, which he has done innumerable times before.
Source: Against Celsus (New Advent)