And it is not matter of surprise that in certain generations there have existed prophets who, in the reception of divine influence, surpassed, by means of their stronger and more powerful (religious) life, other prophets who were their contemporaries, and others also who lived before and after them. And so it is not at all wonderful that there should also have been a time when something of surpassing excellence took up its abode among the human race, and which was distinguished above all that preceded or even that followed.
But there is an element of profound mystery in the account of these things, and one which is incapable of being received by the popular understanding. And in order that these difficulties should be made to disappear, and that the objections raised against the advent of Christ should be answered— viz., that, “after so long a period of time, then, did God now bethink himself of making men live righteous lives, but neglect to do so before?”— it is necessary to touch upon the narrative of the divisions (of the nations), and to make it evident why it was, that “when the Most High divided the nations, when He separated the sons of Adam, He set the bounds of the nations according to the number of the angels of God, and the portion of the Lord was His people Jacob, Israel the cord of His inheritance;” and it will be necessary to state the reason why the birth of each man took place within each particular boundary, under him who obtained the boundary by lot, and how it rightly happened that “the portion of the Lord was His people Jacob, and Israel the cord of His inheritance,” and why formerly the portion of the Lord was His people Jacob, and Israel the cord of His inheritance. But with respect to those who come after, it is said to the Saviour by the Father, “Ask of Me, and I will give You the heathen for Your inheritance, and the uttermost parts of the earth for Your possession.” For there are certain connected and related reasons, bearing upon the different treatment of human souls, which are difficult to state and to investigate.
Source: Against Celsus (New Advent)