Afterwards he says: “If it were possible,” implying at the same time that he thought it most desirable, “that all the inhabitants of Asia, Europe, and Libya, Greeks and Barbarians, all to the uttermost ends of the earth, were to come under one law;” but judging this quite impossible, he adds, “Any one who thinks this possible, knows nothing.” It would require careful consideration and lengthened argument to prove that it is not only possible, but that it will surely come to pass, that all who are endowed with reason shall come under one law.
However, if we must refer to this subject, it will be with great brevity. The Stoics, indeed, hold that, when the strongest of the elements prevails, all things shall be turned into fire. But our belief is, that the Word shall prevail over the entire rational creation, and change every soul into His own perfection; in which state every one, by the mere exercise of his power, will choose what he desires, and obtain what he chooses. For although, in the diseases and wounds of the body, there are some which no medical skill can cure, yet we hold that in the mind there is no evil so strong that it may not be overcome by the Supreme Word and God.
For stronger than all the evils in the soul is the Word, and the healing power that dwells in Him; and this healing He applies, according to the will of God, to every man. The consummation of all things is the destruction of evil, although as to the question whether it shall be so destroyed that it can never anywhere arise again, it is beyond our present purpose to say. Many things are said obscurely in the prophecies on the total destruction of evil, and the restoration to righteousness of every soul; but it will be enough for our present purpose to quote the following passage from Zephaniah: “Prepare and rise early; all the gleanings of their vineyards are destroyed.
Therefore wait upon Me, says the Lord, on the day that I rise up for a testimony; for My determination is to gather the nations, that I may assemble the kings, to pour upon them Mine indignation, even all My fierce anger: for all the earth shall be devoured with the fire of My jealousy. For then will I turn to the people a pure language, that they may all call upon the name of the Lord, to serve Him with one consent. From beyond the rivers of Ethiopia My suppliants, even the daughter of My dispersed, shall bring My offering.
In that day shall you not be ashamed for all your doings, wherein you have transgressed against Me: for then I will take away out of the midst of you them that rejoice in your pride; and you shall no more be haughty because of My holy mountain. I will also leave in the midst of you an afflicted and poor people, and they shall trust in the name of the Lord. The remnant of Israel shall not do iniquity, nor speak lies; neither shall a deceitful tongue be found in their mouth: for they shall feed and lie down, and none shall make them afraid.” I leave it to those who are able, after a careful study of the whole subject, to unfold the meaning of this prophecy, and especially to inquire into the signification of the words, “When the whole earth is destroyed, there will be turned upon the peoples a language according to their race,” as things were before the confusion of tongues.
Let them also carefully consider the promise, that all shall call upon the name of the Lord, and serve Him with one consent; also that all contemptuous reproach shall be taken away, and there shall be no longer any injustice, or vain speech, or a deceitful tongue. And thus much it seemed needful for me to say briefly, and without entering into elaborate details, in answer to the remark of Celsus, that he considered any agreement between the inhabitants of Asia, Europe, and Libya, as well Greeks as Barbarians, was impossible. And perhaps such a result would indeed be impossible to those who are still in the body, but not to those who are released from it.
Source: Against Celsus (New Advent)